Previous HIT Seminars
Tuesday, April 16th, 3:30PM (in-person and on zoom)
Dr. Farid Salazar (University of Washington)
Host: Wenbin Zhao
"Searching for a universal limit of all nuclear matter: Mining for gluon saturation at colliders"
A major pillar of the scientific program of the future Electron-Ion Collider and upcoming upgrades for the Large Hadron Collider is the discovery and characterization of a new regime of nuclear matter, known as color glass condensate (CGC), dominated by a highly dense and saturated system of gluons. Predictions from the CGC effective theory have been confronted with experimental data from HERA, RHIC, and the LHC, where compelling but not definitive signatures of gluon saturation have been observed [1]. The unambiguous determination of this universal limit of all nuclear matter necessitates precise experimental measurements as well as pushing the frontier of theory calculations.
In this seminar, I will review the state-of-the-art precision calculations for various processes in the CGC/saturation formalism. I will focus on our recent work on double [2][3] and single [4] semi-inclusive jet production in deep inelastic scattering, which reveals the need for joint high energy and soft gluon resummation and their interplay to accurately uncover the observable signatures of saturation phenomena in existing and future colliders. If time allows, I will discuss prospects for extending the precision program to a class of observables where the nuclear target remains intact, thus providing a tomographic picture of hadronic and nuclear matter at high energies.
Tuesday, April 9th, 3:30PM (in-person and on zoom)
Dr. Ting-Wai Chiu (National Taiwan University)
Host: Dimitra Pefkou
"Symmetries of spatial correlators of heavy and light mesons in high temperature lattice QCD"
I studied the spatial correlators of mesons in N_f=2+1+1 lattice QCD with optimal domain-wall quarks at the physical point for seven temperatures in the range T ~ 190-1540 MeV. The meson operators include a complete set of Dirac bilinears, and each for six flavor combinations. I discuss their implications for the hierarchic restoration of chiral symmetry from SU(2)_L x SU(2)_R x U(1)_A to SU(3)_L x SU(3)_R xU(1)_A , and to SU(4)_Lx SU(4)_R x U(1)_A , as the temperature is increased from 190 MeV to 1540 MeV, and its impacts to the suppression
of the production heavy mesons in heavy ion collision experiments. Moreover, I discuss the emergence of approximate $SU(2)_{CS}$ symmetry and its physical implications.
Tuesday, April 2nd, 3:30PM (in-person and on zoom)
Dr. Misak Sargsian (Florida International University)
slides Youtube
Host: Shujie Li
"Short Range Nuclear Dynamics Beyond Two-Nucleon Correlations"
With the continuing progress in experimental studies of high energy nuclear processes we are arriving at the point when reliable investigations can be done in probing three-nucleon (3N) short range correlations (SRCs) as well as exploring possible onset of quark degrees of freedom in the nuclear structure at very short distances.
The 3N SRCs are important for realistic modeling of the equation of state of super dense nuclear matter, since such correlations are important in predicting neutron stars above two solar masses.
Probing quark degrees of freedom in short range correlations allows us to understand the limits of nuclear densities at which the nucleonic matter transitions to possible quark matter.
Theoretical approaches in modeling high momentum component of nuclear wave function that includes 3N SRCs and quark degrees of freedom will be discussed. For each phenomena the specific predictions will be presented which can be verified at currently available energies in electron-nuclear scattering processes. Briefly will discuss also possibilities of SRC studies with target fragmentation processes at EIC.
Tuesday, March 26th, 3:30PM (in-person and on zoom)
Dr. Mesut Arslandok (Yale University)
Host: Volker Koch
"Exploring the QCD phase diagram and hunting for new physics via heavy-ion collisions in ALICE at the LHC"
Predictions based on the theory of strong interaction, QCD, imply that, at sufficiently high energy densities, nuclear matter transforms into a state called quark-gluon plasma (QGP), in which quarks and gluons move freely. Ultrarelativistic heavy-ion collisions are ideal environments to study this phase transition, which can be explored via fluctuations of conserved charges such as electric charge, strangeness and baryon number. Moreover, these collisions offer opportunities to probe physics beyond the Standard Model, which will become feasible during the data collection periods of LHC Runs 3 and 4 thanks to the upgraded gas electron multiplier-based time projection chamber of the ALICE detector.
In this talk, I will give an overview of the insights gained from the results of the ALICE collaboration regarding the QCD phase diagram, along with a novel program aimed at searching for new physics beyond the Standard Model utilizing the ALICE TPC. Finally, I will wrap up by discussing the future perspectives of the ALICE collaboration in both of these endeavors, looking
ahead to the future heavy-ion detector, called ALICE3, planned for the early 2030s.
Tuesday, March 19th, 3:30PM (in-person and on zoom)
Dr. Xiang Gao (Physics Division, Argonne National Laboratory)
Host: Wenbin Zhao
"Parton distributions from boosted fields in the Coulomb gauge"
Over the past few years, significant progress has been made in computing parton distributions from lattice QCD within the framework of large momentum effective theory (LaMET). The light-cone parton distributions were derived from gauge-invariant equal-time corrrelators with large momentum boost. In this talk, we introduce a new approach to calculate parton distributions from correlations of boosted quarks and gluons in the Coulomb gauge (CG), without Wilson lines. This new method can substantially improve statistical precision and simplify renormalization, thus providing a more efficient way to calculate parton distributions in lattice QCD, particularly for 3D distributions. We verified the validity of this method at next-to-leading order in perturbation theory and used it to calculate the pion valence quark PDF. Additionally, we derived the Collins-Soper kernel from a CG quasi-TMD up to $b_T$=4.2 GeV^{-1}, further demonstrating its effectiveness and potential for future lattice calculations.
Tuesday, March 12th, 3:30PM (in-person and on zoom)
Dr. Ashish Pandav (Lawrence Berkeley National Lab)
Host: Nu Xu
"High Moments of Net-proton Measurements in STAR at RHIC"
The Quantum-Chromo Dynamics (QCD) phase diagram is the one of strongly interacting matter outlined by temperature, T versus baryon chemical potential μB. It has at least two known phases: the hadronic phase where quarks and gluons are confined, and the QGP phase, where they are deconfined. The quark-hadron phase transition is found to be a smooth crossover at vanishing μB in lattice QCD calculations. At large μB, various QCD-based model calculations predict this to be a first-order phase transition which terminates at a QCD critical point. Neither the presence of QCD critical point (CP), nor the nature of quark-hadron phase transition have been experimentally verified yet.
In the study of QCD phase diagram, fluctuations of conserved quantities, such as net-baryon have been suggested as sensitive observables by theorists. In this regard, the STAR experiment at RHIC performed measurement of net-proton fluctuations (proxy for net-baryon) upto sixth order in phase I of Beam Energy Scan program (BES-I). I will discuss the results and their physics implications in this talk. Recently, the second phase of BES program (BES-II) was concluded which will allow high precision measurement of fluctuations. Prospects and advantages from the BES-II program will also be highlighted.
Tuesday, March 5th, 3:30PM (in-person and on zoom)
Dr. Bigeng Wang (University of Kentucky)
Host: Dimitra Pefkou
"Trace anomaly form factor from lattice QCD"
The hadron mass can be obtained through the calculation of the trace of the energy-momentum tensor (EMT) which includes the trace anomaly and sigma terms. The anomaly due to conformal symmetry breaking is believed to be an important ingredient for hadron mass generation and confinement. For the nucleon, the trace anomaly term is the dominating contribution to its mass. For the pion, the trace anomaly term contributes about half of the mass and approaches zero toward the chiral limit, just like the sigma term due to chiral symmetry breaking. To understand what kind of structure change can facilitate this attribute, the calculation of the spatial distribution of the trace anomaly is necessary.
In this talk, I will present the calculation of the glue trace anomaly form factors of the pion and the nucleon from lattice QCD. By performing a two-dimensional Fourier transform on the form factors in the infinite momentum frame with no energy transfer, we obtain the corresponding spatial distributions.
For the pion, we calculate its mass radius from the glue trace anomaly to be 4.6(0.6)(1.3) fm with possibly large systematic errors. For the nucleon, we calculate its mass radius to be 0.89(10)(07) fm, which is consistent with several recent calculations from gravitational form factors (GFF). We find the pion's spatial distribution changes sign, as does its form factor, for light quark masses. This explains how the trace anomaly contribution to the pion mass approaches zero toward the chiral limit.
arXiv reference: https://arxiv.org/abs/2401.05496
Tuesday, February 27th, 3:30PM ( on zoom)
Dr. Xiaojian Du (Santiago de Compostela U., IGFAE)
Host: Wenbin Zhao
"Non-equilibrium QCD matter and its thermalization"
Non-equilibrium systems and their thermalization are omnipresent in nature. Quark-gluon plasma (QGP), a non-abelian plasma predicted by quantum chromodynamics (QCD) is of particular interest given that its equilibration occurs in nature only during the first few microseconds after the Big Bang. Relativistic heavy-ion collisions (HICs) are the only experiment that can produce this non-equilibrium QCD matter in the laboratory. We will talk about the thermalization of the QCD matter and its application in heavy-ion collision phenomenology. These include QCD turbulence, hydrodynamization and attractor in the thermalization of the QCD plasma, non-equilibrium di-lepton production, and heavy quark thermalization as well as its quantum computing realization.
Thursday, February 22nd, 2:00PM (on zoom and in-person)
Dr. Bhawani Singh (Technical University of Munich)
Host: Nu Xu
“Accessing the Strong Interaction in Three-hadron Systems at the LHC”
Nuclear systems with three hadrons, like unbound ensembles of a deuteron and a hadron, serve as a fundamental reference to constrain nuclear interactions and the properties of nuclei. We present K$^+$–d, p–d as well triplets of hadrons femtoscopic correlations measured by the ALICE Collaboration in proton–proton (pp) collisions at $\sqrt{s} = 13$ TeV at the LHC. It is demonstrated that correlations in momentum space between deuterons and kaons or protons allow us to study three-hadron systems at distances comparable with the proton radius. The analysis of the K$^+$–d correlation shows that the relative distances at which deuterons and proton/kaons are produced are around 2 fm. The analysis of the p–d correlation shows that a comprehensive three-body calculation, accounting for the deuteron's internal structure and short-range nuclear interaction, is crucial to explain the observed correlations. The measurements of p–p–p and p–p–$\Lambda$ correlations provide insights into the underlying two- and three-body effects. The three-body effects have been explored using the cumulant method by subtracting pair-wise interaction contributions in the measured correlation functions.
Tuesday, February 20th, 3:30PM (on zoom)
Dr. Grégoire Pihan (Wayne State University)
Host: Wenbin Zhao
"Tracing the baryon number in relativistic isobar collisions at RHIC"
Traditionally, the baryon number and electric charge within a proton are attributed to the valence quarks. However, a novel conceptualization known as the "baryon junction" challenges this paradigm by proposing that the baryon charge is associated with a Y-shaped, non-perturbative gluonic configuration inside hadrons. Recent preliminary analyses of isobar collisions at the Relativistic Heavy Ion Collider (RHIC) reveal that the scaled net-baryon to net-electric charge number ratio at midrapidity ($B/\Delta Q * \Delta Z/A$) falls within the range of 1.5 to 2. This aligns with predictions derived from the baryon junction model, marking a significant development. This outcome strongly suggests that, in high-energy collisions, the carrier of the baryon number is the baryon junction rather than the valence quarks. However, it is important to note that existing predictions pertain solely to the initial collision stage.
In this seminar I will talk about a comprehensive (3+1)D relativistic hydrodynamic framework incorporating multiple conserved charge currents to systematically investigate this measurement from the initial to the final stage. Simulating the coupled propagation of net baryon and electric charge currents and incorporating a charge-dependent lattice-QCD-based equation of state, we explore the evolution of these charges throughout various phases of heavy-ion collisions. Our findings demonstrate that the aforementioned ratio, as measured in Ru+Ru and Zr+Zr collisions at $\sqrt{s_\mathrm{NN}}=200$ GeV, persists until the final stage, providing quantitative agreement with STAR preliminary measurements.
Tuesday, February 13th, 3:30PM (on zoom)
Dr. Bao-Dong Sun (Ruhr Bochum University)
Host: Dimitra Pefkou
"Exploring Energy-Momentum Tensor Form Factors and Associated Densities"
The electromagnetic form factors of the nucleon have been widely
used for exhibiting how the charge and magnetization distributions
are spatially distributed inside a nucleon in the Breit frame.
Similarly, the Energy-Momentum-Tensor form factors (i.e. gravitational
form factors, GFFs) characterize the mechanical properties, such as
the three-dimensional distributions of mass, angular momentum,
pressure, and shear-force densities inside particles.
In this talk, I will first give a short introduction to GFFs for particles with
different spins and their interpretations in the Breit frame, and I will mention
some of the current experimental measurements or lattice QCD calculations
on GFFs. Next, I will present our recent studies on Delta GFFs and N-Delta
transitional GFFs using the chiral perturbation theory (ChPT) in curved spacetime.
Since the validity of the definitions of local densities in the Breit frame has
been questioned, a new definition using sharply localized wave packet
states is proposed and I will show its application to spin-3/2 systems.
The long-range behaviors of the densities under our newly proposed
definition is obtained with the ChPT results for Delta GFFs.
Thursday, February 1st, 1:00PM (in person)
Dr. Zhong Yang (CCNU)
Host: Andre Walker-Loud
"Quark-gluon plasma and jet-induced medium response in high-energy heavy-ion collisions"
Abstract The jets are powerful probes of quark-gluon plasma (QGP). When a jet loses energy to the QGP medium, it induces the medium response resembling a Mach-cone-like excitation. Investigating this jet-induced medium response can help us to understand QGP properties. We have developed a 2D jet tomography method to localize the initial jet positions and enhance the signal of the jet-induced diffusion wake—an unambiguous part of the medium response. Additionally, we employ a neural network to assist this tomography. To further study the jet-induced diffusion wake, we carry out the simulation of its 3D structure, and investigate its sensitivity to QGP medium properties. We also show that one can use the energy-energy correlators, a novel jet substructure observable, to investigate jet-induced medium response and the short distance structure of QGP in heavy-ion collisions.
Tuesday, January 23th, 3:30PM (on zoom)
Dr. Zaochen Ye (Rice University)
Host: Wenbin Zhao
"Probing Ultra-Dense Gluonic Matter via UPCs at CMS"
Gluons are found to become increasingly dominant constituents of nuclear matter when being probed at higher energies or smaller Bjorken-x values. This has led to the question of the ultimate fate of nuclear gluonic structure and its interaction with external probes at extreme density regimes. In heavy-ion ultraperipheral collisions (UPCs), the coherent heavy-flavor vector meson via photon-nuclear interactions is of particular interest, as its cross section can directly probe the nuclear gluon density function.
In this talk, we will present a new measurement of coherent J/Psi photoproduction with the forward neutron tagging technique in Pb-Pb UPCs at 5.02 TeV. The production cross section will be presented, as a function of the photon-Pb center-of-mass energy per nucleon, up to ~400 GeV, corresponding to an extremely low x of ~6x10-5. We will discuss the physics implications of this new result, as well as exciting opportunities in future LHC heavy ion runs.
Tuesday, January 16th, 3:30PM (in-person and on zoom)
Dr. Yu Hu (Lawrence Berkeley National Lab)
Host: Nu Xu
"Measurements of p-Lambda and d-Lambda Correlations in 3 GeV Au+Au Collisions at STAR"
Heavy-ion collisions provide a unique opportunity to explore nucleon-hyperon (N-Y) interactions through two-particle correlations. The d-Λ correlations shed light on both N-Y two-body and N-N-Y three-body interactions, which is crucial for understanding neutron star properties.
In this talk, we will present the first measurement of d-Λ correlation with √sNN = 3 GeV Au+Au collisions at STAR. Using the Lednicky-Lyuboshitz formalism, we characterize emission source size, the scattering length, and the effective range of d-Λ interactions. The extracted parameters will be compared to those from p-Λ correlations. The physics implications on final state interactions involving hypertriton inner structure will also be briefly discussed.
Tuesday, January 9th, 3:30PM (in-person and on zoom)
Dr. Rajan Gupta (Los Alamos National Lab)
Host: Wenbin Zhao
"The pion-nucleon sigma term from lattice QCD"
This talk presents recent results obtained by the LANL lattice team on the pion-nucleon sigma term, σ_πN, that quantifies the amount of the nucleon mass generated by non-zero up and down quark masses. We show that excited states, in particular multi-hadron Nπ and Nππ states, provide a large contribution. Including these increases σ_πN by almost 50% and reconciles the long-standing difference between lattice results and dispersive methods. Such a larger value increases the reach of direct detection of dark matter by a factor of 2.25 in the scalar channel.
Thursday, December 14th, 10 AM (zoom)
Dr. Eric Voutier (Université Paris-Saclay)
Host: Tyler Hague / Shujie Li
The Jefferson Lab Positron Program
The perspective of high duty-cycle and high intensity polarized and unpolarized positron beams, in complement to the existing CEBAF (Continuous Electron Beam Accelerator Facility) 12 GeV electron beams, has been nurtured since the very first 6 GeV upgrade of the CEBAF accelerator. Along the years, experimental results about the electromagnetic form factors and the generalized parton distributions of the nucleon pointed towards the importance of positron beams for the experimental determination of these fundamental quantities of the nucleon structure. Further ideas emerged about testing the predictions of the standard model, exploring the dark matter sector, or investigating nucleon structure with electroweak processes. A long term and comprehensive research effort has developed both in the physics [1] and the technics [2] areas to assess the potential of an experimental program and to address the technological issues of high duty cycle positron beams. The Jefferson Lab Program Advisory Committee recognized the high scientific value of such a program. The development of positron beam capabilities at Jefferson Lab (JLab) is identified as the first step of a future CEBAF upgrade.
This seminar will review the current status of the JLab positron physics program with a specific focus on Two Photon Exchange effects and the study of Generalized Parton Distributions. The several technical challenges raised by the development of continuous polarized positron beams will be also addressed.
[1] (JLab Positron Working Group) A. Accardi et al. Eur. Phys. J. A 57 (2021) 261.
[2] (Ce + BAF Working Group) J. Grames et al. JACoW IPAC (2023); arXiv/physics.acc-ph:2309.15581.
Tuesday, December 12th, 2023, 3:30 PM PST (in-person & zoom)
Dr. Peter Jacobs (LBL)
Host: Wenbin Zhao
"Low-x evolution at the LHC and EIC: the ALICE FoCal upgrade"
Non-linear evolution of the gluon density of matter at low-x ("gluon saturation") is a natural consequence of the non-Abelian nature of QCD, but quantitative understanding of it remains elusive. The observation and quantification of non-linear evolution would be a major milestone in Nuclear Physics, and its search is a central component of the EIC scientific program. The same QCD forward scattering amplitudes probe saturation effects in both e+A DIS at the EIC and forward p+A at the LHC, providing the opportunity to extend the reach in low-x in this search far beyond the range accessible at the EIC. In this talk I first briefly review the current status of forward QCD measurements at the LHC. I will then discuss the ALICE FoCal ("Forward Calorimeter") upgrade planned for the end of the decade, which will provide incisive measurements of direct photons, neutral and vector mesons, jets, and their correlations, in hadronic and ultra-peripheral pp and p+Pb collisions at forward rapidities, which probe the gluon density down to x~10^-6. Finally, I will discuss a broader strategy for comprehensive analysis of EIC and forward RHIC and LHC data to constrain the low-x gluon distribution.
Monday, December 11th, 3:30 PM (in-person & zoom)
Dr. Raju Venugopalan (BNL)
Host: Dimitra Pefkou
"Universal features of high energy scattering in QCD and gravity from shockwave collisions"
We discuss a remarkable double copy relation (discovered 40 years ago by Lev Lipatov) of multi-particle (2-> N) amplitudes in Einstein gravity to their QCD counterpart. We demonstrate [1] that the results of Lipatov's Feynman diagram computations can be recovered by comparing the inclusive gluon spectrum produced in shockwave collisions in QCD to the inclusive gravitational wave spectrum produced in shockwave collisions in Einstein gravity. We discuss the potential implications of this correspondence both for next-generation measurements of gravitational wave radiation in close Black Hole encounters and for a quantum picture of Black Holes as over-occupied graviton states [2]. The latter description points in turn to a deeper (universal) understanding of gluon shockwaves as Goldstone modes of a broken
global symmetry; their decay in shockwave collisions leads to quark-gluon plasma formation. We discuss the potential implications of this picture for precision computations at the Electron-Ion Collider.
References:
[1] Himanshu Raj and Raju Venugopalan, arXIv:2311.03463
[2] Gia Dvali and Raju Venugopalan, arXiv:2106.11989, Phys. Rev. D105, 056026 (2022).
Thursday, December 7th, 2023 3:30 PM PST (in-person & zoom)
Dr. Gang Wang (UCLA)
Host: Wenbin Zhao
"Review of the Experimental Search for the Chiral Magnetic Effect in Heavy-ion Collisions"
The quark-gluon plasma created in high-energy heavy-ion collisions has been conjectured to exhibit a spontaneous electric-charge separation in the direction of a strong magnetic field through the chiral magnetic effect (CME). The experimental confirmation of the CME in heavy-ion collisions will uncover fundamental aspects of strong interaction physics such as the QCD chiral symmetry restoration and the topological configurations of non-Abelian gauge fields. Over the past two decades, experiments at RHIC and the LHC have performed a series of charge-separation measurements in A+A collisions at various beam energies from the center-of-mass energy of 5.02 TeV down to 7.7 GeV, and in different collision systems including p+Au, p+Pb, d+Au, Cu+Cu, Au+Au, Pb+Pb and U+U collisions, as well as the recent isobaric Ru+Ru and Zr+Zr collisions. Multiple analysis methods have also been developed to manifest the charge separation effect and suppress the flow related background. In this talk, I will review the aforementioned results, summarize our current understanding, and provide an outlook on future analyses.
Tuesday, November 21st, 2023, 3:30 PM PST (in-person & zoom)
Dr. Fernando Romero-Lopez (MIT)
Host: Dimitra Pefkou
"Hadronic resonances from lattice QCD"
The majority of known hadrons in the low-energy QCD spectrum are resonances observed in multi-particle scattering processes. First-principles determinations of the properties of these unstable hadrons are a crucial goal in lattice QCD calculations. Significant progress has been made in developing, implementing, and applying theoretical tools that connect finite-volume lattice QCD quantities to scattering amplitudes, enabling determination of masses and widths of various hadronic resonances. In this talk, I will discuss recent advances in the study of meson-baryon resonances, including the Delta(1232) and Lambda(1405) resonances, as well as three-hadron resonances using lattice QCD.
Monday, November 13th, 2023, 3:30 PM PST (in-person & zoom)
Dr. Paul Caucal (Nantes)
Host: Farid Salazar
"Search for signatures of single hard scattering physics in jet quenching phenomenology"
In a series of publications [1,2], we have proposed a factorized approach, based on perturbative QCD, for the evolution of a jet in a dense quark-gluon plasma, together with its implementation as a Monte-Carlo parton shower and successful applications to the phenomenology of jet quenching. In the original formulation of the parton shower, the collisions between the jet constituents and those of the plasma have been treated in the multiple soft scattering approximation, thus neglecting important effects from single hard scattering. In this talk [3], I will discuss the extension of our Monte Carlo by including the effects of single scattering both on the transverse momentum broadening and on the spectrum for medium-induced radiation. To that aim, the medium-induced cascade is simulated in full 3+1 dimensions and collisions are generated dynamically. This allows us to complete the BDMPS-Z sector of the spectrum for medium-induced radiation with the GLV (Gyulassy-Levai-Vitev) tail at high energies and the Bethe-Heitler spectrum at low energies. Finally, I will discuss an observable that has attracted a lot of attention in recent months: energy-energy correlators. Unlike many jet substructure observables which are dominated by energy loss physics, EEC should display a better sensitivity to single hard scattering effects [4].
Refs:
[1] Caucal, Iancu, Mueller, Soyez, PRL 120 (23), 232001
[2] Caucal, Iancu, Soyez, JHEP 2019 (10), 1-55
[3] Caucal, Iancu, Soyez, in preparation
[4] Barata, Caucal, Monni, Soto-Ontoso, Szafron, in preparation
Thursday, November 9th, 2023, 3:30 PM PST (in-person & zoom)
Dr. Jani Penttala (UCLA)
Host: Farid Salazar
"Exclusive vector meson production at next-to-leading order in the Color Glass Condensate framework"
Exclusive vector meson production is a powerful process to probe the small Bjorken-$x$ structure of protons and nuclei, as such processes are especially sensitive to gluonic structure and also provide access to the spatial distribution of small-$x$ gluons in nuclei. A powerful theoretical framework to study such high-energy processes is the Color Glass Condensate (CGC) effective field theory. So far, most calculations in the CGC framework have been done at the leading order. Recent theoretical developments on the NLO heavy vector meson wave function [1] and the NLO virtual photon light-front wave function [2,3] have made it possible to go beyond the leading order in exclusive vector meson production, allowing us to calculate this process at NLO in the dipole picture for the first time. In this talk, I will discuss the calculation of the NLO corrections to heavy vector meson production in the nonrelativistic limit [4,5], and to light vector meson production in the limit of large photon virtuality [6].
Exclusive vector meson production is a powerful process to probe the small Bjorken-$x$ structure of protons and nuclei, as such processes are especially sensitive to gluonic structure and also provide access to the spatial distribution of small-$x$ gluons in nuclei. A powerful theoretical framework to study such high-energy processes is the Color Glass Condensate (CGC) effective field theory. So far, most calculations in the CGC framework have been done at the leading order. Recent theoretical developments on the NLO heavy vector meson wave function [1] and the NLO virtual photon light-front wave function [2,3] have made it possible to go beyond the leading order in exclusive vector meson production, allowing us to calculate this process at NLO in the dipole picture for the first time. In this talk, I will discuss the calculation of the NLO corrections to heavy vector meson production in the nonrelativistic limit [4,5], and to light vector meson production in the limit of large photon virtuality [6].
[1] M. Escobedo and T. Lappi, Phys.Rev.D 101 (2020) 3, 034030, arXiv:1911.01136 [hep-ph]
[2] G. Beuf, T. Lappi and R. Paatelainen, Phys. Rev.D 104 (2021) 5, 056032, arXiv:2103.14549 [hep-ph]
[3] G. Beuf, T. Lappi and R. Paatelainen, Phys.Rev.D 106 (2022) 3, 034013, arxiv:2204.02486 [hep-ph]
[4] H. Mäntysaari and J. Penttala, Phys. Lett.B 823 (2021), 136723, arXiv:2104.02349 [hep-ph]
[5] H. Mäntysaari and J. Penttala, JHEP 8 (2022) 247, arXiv:2204.14031 [hep-ph]
[6] H. Mäntysaari and J. Penttala, Phys.Rev.D 105 (2022) 114038, arXiv:2203.16911 [hep-ph]
Tuesday, October 31st, 2023, 3:30 PM PST (in-person & zoom)
Dr. Shohini Bhattacharya (BNL)
Host: Farid Salazar
"Generalized TMDs and GPDs: Recent Advances"
The presentation will be structured into two distinct parts. In the first part, I will talk about Generalized TMDs (GTMDs), whose fourier transforms can be related to the Wigner functions. I will offer a concise overview of GTMDs, providing insights into their significance and the remarkable developments that have unfolded in recent years. Of particular focus will be the current state-of-the-art observables associated with these quantities. The second part of this presentation will pivot to Generalized Parton Distributions (GPDs). Recent advancements have opened doors to the approximate computation of light-cone correlation functions in lattice QCD through the evaluation of Euclidean correlation functions. In this segment, I will provide a brief exploration of these recent breakthroughs and then transition to our most recent work. Specifically, I will discuss our novel formalism designed to enhance the efficiency of lattice calculations related to GPDs, shedding light on the innovative theoretical approaches we have developed.
Tuesday, October 24th, 2023, 3:30 PM PST (in-person and zoom)
Dr. Yuanjing Ji (LBL)
Host: Shujie Li
"Measurements of Hypernuclei Production and Their Properties in Heavy-Ion Collisions at STAR"
Hypernuclei are bound states of nuclei with one or more hyperons. They introduce additional degree of freedom in nucleon interactions, the hyperon-nucleon Y-N interaction, which is an important ingredient for the equation-of-state (EoS) of dense nuclear matter. Precise measurements of hypernuclei properties and their production yields in heavy-ion collisions are crucial for the understanding of the strength of the Y-N interaction and their production mechanisms. The strangeness population factor, S3 = (H3L/^{3}He)(p/Lambda) (and S4), is of particular interest as it directly relates to the ratio of light nuclei and hypernuclei coalescence parameters. Moreover, it is suggested that S3(S4) might be sensitive to the onset of deconfinement. The STAR Beam Energy Scan II program and isobar collisions offer a great opportunity to investigate energy and system size dependence of hypernuclei production. In this talk, I will review measurements of hypernuclei production, collectivity, and their intrinsic properties at STAR. The physics implications on the hypernuclei production mechanism and properties of Y-N interaction will be discussed.
Tuesday, October 17th, 2023, 3:30 PM PST (zoom)
Dr. Toshiyuki Gogami (Kyoto University)
Host: Shujie Li
"Physics in Lifetime and Energy of Lambda Hypernuclei"
A hypernuclear study is a powerful tool to investigate the strong interaction between baryons with strangeness degrees of freedom. The strange baryon interaction is necessary to construct equation of states of neutron stars. There are only about 40 species of observed hypernuclei. The fact of lacking data leads to many puzzles which many scientists tackle to solve. A confliction between a short lifetime and a small binding energy of the simplest hypernucleus, hypertriton, is one of puzzles. Recently, lifetime measurements of hypernuclei by heavy ion beams/collisions successfully provided new data at BNL, CERN, and GSI. I will overview a progress of hypernuclear physics based on recent experimental results. In addition, I will introduce future hypernuclear experiments planned at J-PARC (Japan) and Jefferson Lab (US) in which high intensity hadron and electron beams are used, respectively.
Tuesday, October 10th, 2023, 3:30 PM PST (in-person & zoom)
Dr. Yuxun Guo (LBL)
Host: Farid Salazar
"Probing the gravitational form factors of the nucleon from near threshold heavy quarkonium photo-production"
The gravitational form factors (GFFs) are one of most fundamental quantities that carry information about the mechanic properties such as the mass and spin of the nucleon. Probing them, on the other hand, has been experimentally challenging due to the weak gravitational coupling of the nucleon. The generalized parton distribution (GPD) not only offers an alternative way to access these GFFs, but can also provides further information of the 3D structure of the nucleons, and therefore has captivated rising interest. In this talk, I will discuss our recent work on the near threshold heavy quarkonium photo-production in the GPD framework. I will talk about how the GFFs can be constrained/extracted from such processes in the large skewness limit and discuss the recent measurements of by the experimental groups at JLab as an example.
Thursday, September 21st, 2023, 3:30 PM PST (zoom)
Dr. Renaud Boussarie (CPHT, Ecole Polytechnique)
Host: Farid Salazar
"Exclusive Compton scattering processes from low to moderate x"
In QCD observables at very high energies, or equivalently at low values of the Bjorken x variable, gluonic saturation effects are taken into account by semi-classical effective theories such as the Color Glass Condensate theory. Higher loop corrections to several such observables have recently been computed, but they highlighted instability issues due to collinear logarithms. While many ad hoc schemes have been developed in order to address this, the deeper reason for these instabilities remains unaddressed. In this seminar, we will discuss an attempt at correcting this deeper problem via a minimal correction to the semi-classical effective theories. We will apply it to the exclusive Compton scattering amplitude and obtain an interpolating formula between its high and moderate energy descriptions, then we will discuss its implications.
Tuesday, September 19th, 2023, Special time 2:00 PM PDT (in-person & zoom)
Joint Nuclear Theory/HIT seminar
Dr. Georg Wolschin (Heidelberg University)
Host: Farid Salazar
"Stages of relativistic heavy-ion collisions"
An analytically solvable nonlinear diffusion model is presented to account for the fast thermalization of quarks and gluons. It is compared with numerical results of QCD-based theories for Pb-Pb collisions at LHC energies. Stopping of the interpenetrating fragments as measured through net-proton rapidity distributions at SPS and RHIC energies is described in a time-dependent nonequilibrium-statistical model that is consistent with QCD. The net-proton rapidity distributions of the individual fragments exhibit a scaling behaviour similar to limiting fragmentation that is related to geometric scaling in the color glass condensate and depends upon the gluon saturation scale. Comparisons with SPS and RHIC data are presented, predictions for LHC are made. The consideration of charged-hadron production requires a third (fireball) source for particle production, which is treated in a two-dimensional relativistic diffusion model for transverse and longitudinal rapidity. The underlying Fokker-Planck equation is derived from a general Lorentz-invariant stochastic theory. With a fluctuation-dissipation theorem adapted to the proper initial and final distributions, the time-dependence of particle production is computed. Charged-hadron distribution functions in transverse momentum and pseudorapidity are compared with recent LHC data from ALICE and ATLAS.
[1] G. Wolschin, EPL 140, 40002 (2022); Physica A 597, 127299 (2022)
[2] J. Hoelck, G. Wolschin, Phys. Rev. Res. 2, 033409 (2020)
[3] T. Bartsch, G. Wolschin, Annals of Physics 400, 21 (2019)
[4] J. Hoelck, E. Hiyama, G. Wolschin, Phys. Lett. B 840, 137866 (2023)
[5] J. Hoelck, G. Wolschin, submitted to Ann. Physik (2023)
Friday, August 4th, 2023, 3:00 PM PST (in-person & zoom)
Dr. Joao Barata (BNL)
Host: Farid Salazar
Quantum to classical dynamics in the QGP
When evolving in the quark gluon plasma (QGP), hard probes such as jets get modified due to the interactions with the underlying nuclear matter. As the jet evolves, the interactions with the medium decohere the system, such that at late times certain correlations of the initial state have been washed out. However, the exact way this occurs for a full shower is not known at this moment. In this talk I will give a first step in this direction and discuss the time evolution of the density matrix of a high energy quark in the presence of a dense QCD background. We observe that the quark state loses all memory of the initial condition and the reduced density matrix satisfies Boltzmann-diffusion transport. As a result, the density matrix can be interpreted as a classical phase space distribution, with the entropy of the state showing the transition between a quantum and classical region. Finally, I will also show recent amplitude level simulations, which confirm some of these analytical results.
Tuesday, June 27, 2023 3:30 PM PST (zoom)
Dr. Chiara Bissolotti (ANL)
Host: Jennifer Rittenhouse West
Unpolarized Transverse Momentum Distributions from a global fit at N3LL
Transverse Momentum Distributions (TMDs) are three-dimensional maps of hadrons in momentum space and generalize the well-known concept of collinear Parton Distribution Functions (PDFs). TMDs are crucial in understanding the 3D spin and momentum structure of the nucleon and other hadrons, and information on their functional form can be obtained, for example, from Drell-Yan and Semi-Inclusive Deep Inelastic Scattering (SIDIS).
In this seminar I will discuss the state-of-the art status of unpolarized TMD extractions, focusing on the results obtained by the MAP Collaboration and in particular on the most recent global TMD extraction that reaches the perturbative accuracy of next-to-next-to-next leading log.
Our analysis is performed in the TMD factorization framework and is based on data from several experiments and kinematic ranges.
I’ll also discuss the introduction of (pre-computed) normalization coefficients for SIDIS data. The fit is performed taking into account correlated and uncorrelated uncertainties and we found that present data are very well described by our choice of non-perturbative functions.
Tuesday, June 20th, 2023 3:30 PM PST (zoom)
Dr. Sylvester Joosten (ANL)
Host: Shujie Li
Heavy Quarkonium Production: Decoding the Gluonic Structure of the Nucleon and the Dynamic Origin of its Mass
Heavy quarkonium production offers a unique avenue to probe the gluonic structure of the nucleon. The latest generation of experiments at Jefferson Lab in the 12 GeV era use near-threshold J/ψ production to explore topics related to the dynamic origin of nucleon mass, the nature of the color Van der Waals force, and the existence of the LHCb charmed pentaquark. These topics can be further studied at the upcoming electron-ion collider (EIC) through near-threshold Y production. Significantly, the EIC promises access to the full three-dimensional tomographic image of the gluonic structure of the nucleon through J/ψ and Y production at high energies. In this seminar, I will highlight my J/ψ experiment in Hall C, including our recent work on determining mass radius of the proton. I will then discuss future opportunities with the SoLID experiment and at the EIC.
Tuesday, June 13th, 2023 3:30 PM PST (in-person & zoom)
Dr. Wei-yao Ke (LANL)
Host: Farid Salazar
Parton Shower in Cold Nuclear Matter: Monte Carlo and Theory Developments
The physics program at the future electron-ion colliders propels tremendous progress in both the theory and practical simulation tools to understand parton propagations in cold nuclear matter. I will first talk about endeavors in developing the eHIJING event generator [1]. I will focus on the physics of medium-modified parton shower and fragmentation in electron-ion collisions, review its phenomenological applications, and discuss its future perspective. In the second half of the talk, I will introduce a recent theoretical work that provides an analytical understanding of medium-modified hadron fragmentation [2] and discuss its implications for Monte Carlo event generators with medium effects.
[1] WK, Y. Zhang, H. Xing, and X.-N. Wang 2304.10779
[2] WK, I. Vitev 2301.11940
Tuesday, May 23rd, 2023 3:30 PM PST
Dr. Ronen Weiss (LANL)
Hosts: Jennifer Rittenhouse West
Short-range expansion and three-nucleon correlations in nuclear systems
An accurate description of short-range physics is one of the main challenges in the study of strongly interacting many-body quantum systems. In nuclear systems, short-range correlations (SRCs) have been studied extensively in the last decades using both large momentum transfer quasi-elastic reactions and ab-initio calculations. In this talk, I will present an overview of the Generalized Contact Formalism, an effective model based on the short-range factorization of the many-body wave function, that allows to obtain a comprehensive picture of the effects of SRCs in nuclei. I will then discuss recent results in which first signature of three-nucleon correlations is observed. I will also present an extension of the formalism which includes sub-leading corrections to the wave-function factorization, towards a systematic short-range expansion of the nuclear many-body problem. Finally, I will show an application for the calculation of neutrinoless double beta decay matrix elements.
Tuesday, May 16th, 2023 3:30 PM PST (zoom & in person)
Dr. Wenqing Fan (LBNL)
Host: Jennifer Rittenhouse West
Studying jet substructure with energy correlators at colliders
Abstract: The internal structure (substructure) of jets produced in high-energy hadron collisions encodes rich Quantum Chromodynamics (QCD) dynamics, from the interaction of quarks and gluons in the weakly coupled limit to the hadronization process in the strongly coupled limit. Studies on jet substructures have attracted interest from both the theoretical and experimental sides, together advancing our understanding of QCD. Central to the recent development of jet substructure has been the use of energy correlators, which measure statistical correlations of the energy flux within a jet. Defined as the energy-weighted cross-section of particle pairs inside jets, one unique advantage of the energy-energy correlator (EEC) over other jet substructure measurements is that they provide a calibrated probe of the scale dependence of QCD dynamics in vacuum, where the scale is controlled by the angular distance of the pairs. If one looks at the scaling behavior of the EEC as a function of pair distance, there is a perturbative regime at large angular distance and a non-perturbative (NP) regime at small angular distance. Such a distinct separation of the perturbative from the non-perturbative regime allows us to probe the dynamics of jet formation and their confinement into hadrons. In this talk, I will discuss the EEC measurements with inclusive jets in pp collisions at the LHC. From the pp measurements, the separation of the perturbative and NP region is clearly seen. Moreover, a transition region with a turn-over behavior occurs, which corresponds to the confinement process. I will also show how this observable can be used in eA collisions at the future EIC to image the scales of nuclear size and study the jet-medium interaction as a function of nuclear size.
Tuesday, May 9, 2023 3:30 PM PST (zoom)
Dr. Jimmy Caylor (Jefferson Lab)
Host: Jennifer Rittenhouse West
"Overview of Neutron Lifetime Measurement Methods"
Precision measurements of neutron beta decay can provide answers to some of the most fundamental questions in particle physics, astrophysics and cosmology. Neutron beta decay, a semi-leptonic decay, is the simplest form of nuclear beta decay; therefore, it provides a clean test of the weak interaction of the Standard Model (SM). A precise measurement of the neutron lifetime and λ, the ratio of axial vector and vector coupling constants of the weak interaction, allows for a determination of the Cabibbo-Kobayashi-Moskawa (CKM) matrix element V ud that is free from nuclear structure effects. The SM predicts that the CKM matrix is unitary; therefore, the measurement of the neutron lifetime provides an important test of the SM. The neutron lifetime is also an important input parameter into early universe Big Bang nucleosynthesis calculations, as well as playing a role in other areas including solar physics and the detection of reactor antineutrinos. Two main methods have been developed to measure the neutron lifetime: the “bottle” method and the “beam” method. In the bottle method, ultracold neutrons are confined in a material and/or magnetic trap. Ultracold neutrons are loaded into the trap and after varying periods of time the remaining number of neutrons are counted. In the beam method, a cold neutron beam passes through a fiducial decay volume. The absolute neutron beam flux is measured, as well as the absolute number of decay particles (protons or electrons) resulting from neutron decay inside the fiducial volume. The most precise neutron lifetime measurements have reached uncertainties of less than 1 s; however, there remains significant scatter in the results. A large, 4 σ, discrepancy exists between the bottle weighted mean and the beam weighted mean for the neutron lifetime. An overview of the experimental methods, ongoing and future experiments will be discussed with particular emphasis on systematic tests of the beam method.
Thursday, May 4th, 2023 3:30 PM PST (in-person & zoom)
Dr. Niveditha Ramasubramanian (CEA, Saclay)
Host: Wenqing Fan, Farid Salazar
"Disentangling centrality bias and final state effects in small system collisions"
PHENIX conducted a study on d+Au collisions at 200GeV to investigate the centrality binned nuclear modification factor of Pi0. The results showed a suppression in the Pi0 yield for most central events, which is consistent with the formation of QGP droplets in small systems. However, a strange enhancement was observed in peripheral collisions To rule out possible biases in centrality determination due to energy loss, PHENIX measured the yields of high pT Pi0 and direct photons in different bins of event activity. The ratio of direct photons to Pi0 for different centrality classes was found to be consistent with minimum bias and with the ratio observed in p+p collisions, except for the most central events To further investigate the final state effects, a double ratio was defined by normalizing the Pi0 nuclear modification factor with that of direct photons. As the initial state effects are expected to be similar for the production of Pi0 and direct photons, they cancel in this double ratio, providing a clean signal to study the final state effects. The results showed a 20% suppression with a 4.5 sigma confidence for most central events compared to minimum bias, while there was a strong agreement between peripheral events and minimum bias.
Tuesday, April 25th, 2023 3:30 PM PST (zoom)
Dr. Norbert Herrmann (Heidelberg University)
Host: Nu Xu
"The CBM Experiment at FAIR: Physics Perspectives and Status"
The Compressed Baryonic Matter (CBM) experiment is one of the major scientific pillars of the Facility for Antiproton and Ion Research (FAIR), which is expected to become operational in 2028-29. The goal of CBM is to explore the QCD phase diagram in the region of high baryon densities using nucleus-nucleus collisions in the energy range sqrt(s_NN) = 2.9 - 4.9 GeV. CBM will be utilizing peak interaction rates of up to 10 MHz and an advanced triggerless data acquisition scheme, giving access to rare physics probes not studied before. This contribution will give an overview of the CBM physics goals among which the equation-of-state of dense nuclear matter, the possible phase transition from hadronic to partonic phase, and chiral symmetry restoration play a major role. The CBM physics performance in terms of (multi-) strange particle production, dilepton spectroscopy, collective flow will be discussed with a focus on sensitivity to criticality and first order phase transitions. In addition, the status of the comprising detector sub-systems will be presented. This includes their performance in FAIR Phase-0 experiments, especially in the currently operated demonstrator mCBM at SIS18.
Tuesday, April 18th, 2023 3:30 PM PST (zoom)
Dr. Jian Zhou (Shandong University)
Host: Farid Salazar
"Gluon tomography with UPCs"
Linearly polarized coherent photons excited by a charged ultra-relativistic nucleus is proven to be a powerful experimental tool to explore the gluon tomography. We show that various azimuthal asymmetries in diffractive ρ 0 production observed in ultraperipheral heavy ion collisions by STAR collaboration arise from the linear polarization of photons. More interestingly, the cos 2ϕ asymmetry provides a unique chance to study the double slit interference effect in high energy scatterings, while the observation of the cos 4ϕ asymmetry might signal the existence of the nontrivial correlation in quantum phase distribution of gluons.
Tuesday, April 4th, 2023 3:30 PM PST (zoom)
Dr. John Terry (LANL)
Host: Farid Salazar
"TMD Factorization and Resummation at NLO+NLP"
Transverse momentum-dependent distributions (TMDs) provide three-dimensional information for the spin-dependent structure of partons in hadrons, allowing us to connect parton dynamics with the global properties of hadrons. In the past decade, advancements in TMD factorization and resummation formalisms have led to enormous developments in the three-dimensional imaging of hadrons. Canonically, TMD formalisms have focused on leading-power (LP) effects, which are governed by correlation functions of two partons. Next-to-leading-power (NLP) corrections provide information for novel distributions, including multi-parton correlation functions. In this talk, I’ll present our recent formalism for factorizing the NLP cross-section and perturbative calculating the hard, soft, and collinear contributions up to one loop. I’ll demonstrate the LP and NLP distributions mix at one loop and give rise to anomalous dimension matrices. Further, I’ll discuss the one-loop matching of the NLP TMDs.
Tuesday, March 21, 2023 3:30 PM PST (zoom)
Dr. Jihee Kim (Argonne)
Host: Jennifer Rittenhouse West
"Design Concept of Imaging Barrel Electromagnetic Calorimeter for the Electron-Ion Collider"
The Electron-Ion Collider (EIC) will be an experimental facility to explore the gluons in nucleons and nuclei, shedding light on their structure and the interactions within. Physics goals, detector requirements, and technologies at the EIC are outlined and discussed in the EIC community White Paper and Yellow Report. In particular, for the barrel electromagnetic calorimetry, the electron energy and shower profile measurements play a crucial role in the separation of electrons from background pions in deep inelastic scattering processes. Moreover, the calorimeter must measure the energy and position of photons, identify single photons originating from deeply virtual compton scattering process, and photon pairs from pi^0 decays. Based on detector requirements, we propose a design of the imaging barrel electromagnetic calorimeter. It is a hybrid design utilizing imaging calorimetry based on monolithic silicon sensors (AstroPix) and scintillating fibers embedded in Pb. We have studied the proposed calorimeter in detail through realistic simulations to test it against the requirements for the physics case described in the EIC community Yellow Report. In this talk, I will present the expected calorimeter performance based on simulations with 3T magnetic field and the outlook of the upcoming R&D program related to the imaging calorimetry will be also presented.
Special date & room - same time!
Thursday, March 16, 2023 3:30 PM PST (in-person & zoom) Room 70-191
Dr. Ian Moult (Yale University)
Host: Wenqing Fan
"Conformal Colliders Meet the LHC"
Jets of hadrons produced at high-energy colliders provide experimental access to the dynamics of asymptotically free quarks and gluons and their confinement into hadrons. Motivated by recent developments in conformal field theory, we propose a reformulation of jet substructure as the study of correlation functions of a specific class of light-ray operators and their associated operator product expansion (OPE). We show that multi-point correlation functions of these operators can be measured in real LHC data, allowing us to experimentally verify properties of the light-ray OPE. We then discuss how this reformulation provides new ways of experimentally studying QCD at colliders, as well as new theoretical techniques for performing previously intractable calculations.
Tuesday, March 14th, 2023 3:30 PM PST (zoom)
Dr. Jianwei Qiu (Jefferson Lab)
Host: Farid Salazar
"Exclusive hard processes for extracting Generalized Parton Distributions"
The Generalized Parton Distributions (GPDs) describe the distribution of quarks/gluons inside a colliding hadron in both longitudinal partonic momentum fraction $x$ and transverse space (“tomographic images”). Their moments of the momentum fraction $x$ provide critical information on partonic angular momentum contribution to the hadron spin and gravitational form factors of the hadron. Extracting GPDs reliably from experimental measurements has been a major science goal for studying QCD and hadron physics. However, conventional exclusive processes such as deeply-virtual Compton scattering (DVCS) cannot fully disentangle the longitudinal dependence and provide the tomographic images at fixed x. In this talk, I will introduce a class of exclusive hard processes, to be referred as single diffractive hard exclusive processes (SDHEP), for the extraction of GPDs. I will discuss the necessary and sufficient conditions for SDHEP to be factorized in terms of GPDs. I will also demonstrate that SDHEP is not only sufficiently generic to cover all known processes for extracting GPDs, but also well-motivated for the search of new processes for the study of GPDs. Finally, I will carefully examine the sensitivity of SDHEP to the parton momentum fraction $x$ dependence of GPDs.
Tuesday, March 7th, 2023 3:30 PM PST (in-person & zoom)
Dr. Haiyan Gao ( BNL and Duke University )
Host: Shujie Li
"Physics Program with SoLID"
The Solenoidal Large Intensity Device (SoLID) is a new experimental apparatus proposed for Hall A at the Thomas Jefferson National Accelerator Facility (JLab). SoLID will combine large angular and momentum acceptance with the capability to handle high data rates at large luminosity. As such SoLID will push JLab to a new limit at the QCD intensity frontier to exploit the full scientific potential of the 12-GeV CEBAF. The slate of approved high-impact experiments consists of the tomography of the nucleon in 3-D momentum space from Semi-Inclusive Deep Inelastic Scattering, expanding the phase space in the search for new physics and novel hadronic effects from parity-violating Deep Inelastic Scattering, a precision measurement of near-threshold J/psi production to probe the gluon field and its contribution to the proton mass, and more. In this talk, I will discuss the rich SoLID physics program and the proposed apparatus.
Change in time & location:
Thursday, March 2, 2023 1 PM PST (in-person & zoom) Nuclear theory seminar room!
Dr. Agnieszka Sorensen (University of Washington)
Host: Jennifer Rittenhouse West
"The equation of state of dense nuclear matter from heavy-ion collisions"
The equation of state (EOS) of dense nuclear matter can give insights into fundamental properties of QCD: among others, it can elucidate phases of matter in different regions of the QCD phase diagram, it can help explain the structure of both neutron stars and neutron-rich nuclei, and it can inform us about the nature of the underlying fundamental interactions. In experiments colliding heavy nuclei at relativistic velocities, the EOS is probed through observables describing the collective behavior of the produced matter, such as flow observables, the dependence of which on the EOS can be studied in simulations. In this talk, I will discuss recent progress on constraining the EOS with hadronic transport simulations, used to model heavy-ion collision experiments at intermediate energies. I will highlight results from a recent Bayesian analysis study using new data from RHIC, and I will discuss the findings in the context of other known constraints from heavy-ion collisions and neutron star studies. I will also outline developments in state-of-the-art hadronic transport codes necessary to fully utilize the potential of the forthcoming wealth of data from the BES-II FXT program at RHIC, from GSI and FAIR, as well as from FRIB and future FRIB400.
Tuesday, February 28th, 2023 3:30 PM PST (in-person & zoom)
Christopher Kane (University of Arizona)
Host: Christian Bauer, Farid Salazar
"Overcoming exponential volume scaling in quantum simulations of lattice gauge theories"
Quantum computers hold the promise of overcoming the numerical sign problem and allowing for study of the dynamics of quantum field theories from first principles. Before performing such calculations, it is important to ensure that the quantum algorithms used do not have a cost that scales exponentially with the volume. In this talk, I will discuss an interesting test case: a formulation of compact U(1) gauge theory in 2+1 dimensions free of gauge redundancies. A naive implementation onto a quantum circuit has a gate count that scales exponentially with the volume. I will discuss how to break this exponential scaling by performing an operator redefinition that reduces the non-locality of the Hamiltonian. With the exponential volume scaling broken, I will then show how the gate count scaling with the volume can be further reduced by approximating the quantum circuit without introducing large errors.
New Special time: Tuesday, February 14, 2023, 9:30 AM PST (Zoom)
Dr. Yousen Zhang (Rice University)
Host: Peter Jacobs and Farid Salazar
Slides and Recording available upon request to organizers
"Probing QCD matters using heavy flavor quarks at the LHC"
Quark gluon plasma created in relativistic heavy ion collisions is a novel state in which partons are deconfined from normal matter in the universe. It is characterized by the shocking collectivity of QGP and energy loss of high energy particles traversing through QGP. Recent measurements show that the collectivity can also emerge in high-multiplicity proton-proton and proton-nucleus collisions, which was originally believed to only exist in large ion collisions. However, the origin of these collective motions is still a puzzle in theoretical studies mainly debating on contributions from initial correlations and in-medium effects. Heavy flavor quarks are sensitive to both the initial stage conditions and the later-on in-medium effects of collisions, thus can provide important information for understanding the inner workings of QGP in large ion collisions and the origin of the collectivity in small systems. In this talk, I will present the recent progress of heavy flavor collectivity at the LHC from large to small colliding systems, and discuss the future opportunities with the high-luminosity LHC together with the CMS detector upgrades.
Special time: Thursday, February 9, 2023, 2:00 PM PST (Zoom)
Dr. Nicole Lewis (Brookhaven)
Host: Peter Jacobs and Shujie Li
"Baryon Stopping in Photonuclear Collisions"
Photonuclear collisions are one of the simplest processes that can happen in a heavy-ion collision. They occur when one nucleus emits a quasi-real photon which interacts with the other colliding nucleus, similar to an electron-ion collision except that the photon tends to have a much smaller virtuality. Photonuclear collisions can be used to study bulk properties of the medium such as collectivity due to initial-state effects and hadron chemistry. In these photonuclear collisions we observed baryon stopping: more baryons that antibaryons even at midrapidity. This phenomenon is well documented in proton-proton and heavy-ion collisions, but it is not well understood and had never before been seen in photonuclear collisions. This could indicate the existence of a baryon junction within the nucleon, a nonperturbative Y-shaped configuration of gluons which carries the baryon number and is attached to all three valence quarks. These measurements will also inform future measurements using particle identification at the upcoming Electron Ion Collider.
"Probing nonlinear gluon dynamics at RHIC and the EIC"
The gluon distribution function grows with lower and lower momentum fraction very fast. As the total scattering cross section is bound by quantum mechanics, the raise of the gluon density has to be tamed, which is explained by gluon recombination under the color glass condensate (CGC) framework. A definitive discovery of nonlinear effects in QCD and as such the saturation regime would significantly improve our understanding of the nucleon structure and of nuclear interactions at high energy. Two particle azimuthal correlation is one of the most direct and sensitive channels to access the underlying nonlinear gluon dynamics. In this talk, we will present the recent results of forward di-hadron correlations measured at RHIC, together with the signatures of gluon saturation predicted by CGC. New opportunities for measurements with the STAR forward upgrade and future EIC to study the nonlinear effects in QCD will also be discussed.
Special date & time: Thursday, February 2, 2023, 10:30 AM PST (Zoom)
Florian Jonas (University of Münster/ORNL)
Host: Peter Jacobs and Farid Salazar
Slides and Recording available upon request to organizers
"Prompt photon production: probing gluons in protons and nuclei at hadron colliders"
Measurements of prompt photons at hadron colliders offer unique insights into the substructure of the colliding projectiles, enabling constraints of so called Parton Distribution Functions (PDFs), which encode the inner structure of the hadron in a universal parametrization.
In particular, prompt photons are sensitive to the gluon distributions, which are one of the least constrained PDFs and not directly accessible via deep inelastic scattering.
Furthermore, studies of the gluon bound inside protons (and nuclei) are of key importance for the exploration of non-linear QCD, where in particular their low-x growth is expected to be tamed by gluon saturation.
Photons do not interact via the strong interaction, which makes them a particularly robust probe, carrying information from the initial hard scattering to the detector, unaffected by any final state effects commonly encountered in large collision system.
This talk outlines the key experimental techniques and challenges arising in isolated prompt photon measurements. An overview of the currently available experimental results at the LHC and their impact on the gluon PDF is followed by a look into the future, outlining how prompt photon measurements at hadron colliders with the ALICE Forward Calorimeter can play an important role in the search for gluon saturation and complement DIS measurements at the EIC.
Special seminar on Wednesday:
Wednesday, January 18th, 2023, 3:30 PM PST
Dr. Xiaohui Liu (Beijing)
Host: Jennifer Rittenhouse West
"Nucleon Energy Correlators for the Color Glass Condensate"
An invited talk and discussion on very recent work by Xiaohui Liu, Feng Yuan and collaborators on low-x physics, specifically a new method to access gluon saturation which is highly relevant for the future Electron-Ion Collider. All welcome, and please note this will be a pedagogical seminar with a combination of slides and whiteboard, particularly aimed toward early career people who might not be familiar with the physics.
Tuesday, January 17th, 2023, 3:30 PM PST
Dr. Adam Freese (U. Washington)
Host: Jennifer Rittenhouse West
"Spatial distributions of energy and stresses in hadrons"
The Lorentz group of special relativity contains a Galilean subgroup, which manifests in the light front picture of spacetime. Light front coordinates thus allow a fully relativistic spatial description of the internal structure and dynamics of hadrons, specifically in the form of two-dimensional densities on the plane transverse to the observer's line of sight. The energy-momentum tensor allows distributions of energy, momentum, spin and stresses to be obtained. In this talk, I elaborate on the physical meaning of light front coordinates, and explain the formalism for determining internal distributions of hadrons. Concrete model examples for the internal structure of mesons are provided.
Tuesday, January 10th, 2023, 3:30 PM PST (in-person & zoom)
Dr. Joao Barata (BNL)
Host: Farid Salazar/Xin-Nian Wang
Jet evolution in anisotropic plasmas
Over the last decades, the heavy-ion collisions at RHIC and the LHC allowed the exploration of QCD at high energies and densities. In these experiments, the nuclear matter is produced far from equilibrium, and undergoes a multiphase evolution until it thermalizes into a nearly ideal liquid: the quark-gluon plasma (QGP). The main effort of the heavy-ions community is focused in extracting the detailed properties of this phase of matter. Among the many probes used for this effect, QCD jets have proven to be able to explore the quark gluon plasma at different time and length scales, providing a differential and dynamical picture for the underlying matter. Nonetheless, a theoretical treatment of jet structure which is sensitive to the details of the QGP is still far from complete. In this talk, I will present some recent work on how to describe jet evolution in the presence of anisotropic matter. First, I will detail the basic modifications necessary to make to the standard jet quenching formalism. Afterwards, I will show that the QGP anisotropies can be taken into account to arbitrary order in a gradient expansion using an effective kinetic theory approach. Remarkably, at second order in the matter gradients, we find a novel master equation which generalizes the usual Boltzmann transport. Finally, I will discuss how such effects can be manifest at the level of jet observables.
Thursday, December 15th, 2022 3:30 PM PST (zoom)
Dr. Alba Soto-Ontoso (CERN)
Host: Farid Salazar
"Better parton showers for HL-LHC and beyond"
The Large Hadron Collider is currently running at its highest energy and luminosity. In order to maximally exploit the potential of this precise dataset to uncover physics beyond the Standard Model, it is of crucial importance to develop tools that faithfully characterise the QCD background. Parton showers lie at the core of general purpose Monte Carlo event generators. They aim at correctly describing the phase-space for QCD branchings across disparate energy scales. A natural question, largely overlooked in the literature, is up to which degree of logarithmic accuracy do parton showers meet this goal. In this talk, I will introduce recent efforts by the PanScales collaboration to establish the criteria that a parton shower should satisfy in order to reach a given logarithmic accuracy. Then, I will present the design and implementation of next-to-leading logarithmic accurate parton showers both in electron-positron annihilation and hadron collisions. I will conclude with some exploratory studies about the phenomenological impact of these highly-precise showers.
Tuesday, December 13th, 2022 3:30 PM PST (zoom)
Dr. Allison Zec (UNH)
Host: Jennifer Rittenhouse West
"Achieving High Deuteron Tensor Polarization To Probe Nuclear Structure"
Advances in experimental technology have allowed for new high-luminosity scattering probes on highly spin polarized nuclear targets. These developments have made it possible to probe the structure of tensor-polarized deuterium with greater precision than ever before. Two experiments, approved to run in Jefferson Lab's experimental hall C will measure two deuteron tensor observables. The first experiment will probe the deuteron tensor structure function b1 in the x<1 deep inelastic region, and the second experiment will measure the deuteron tensor asymmetry Azz in the quasielastic region. In order to achieve a high tensor polarized deuteron target, developments are being made in nuclear polarization technology using the dynamic nuclear polarization (DNP) technique. DNP is used to enhance the nuclear spin polarization of materials. DNP works by using microwaves to continuously drive spin transitions in a material that is doped with free radicals and placed inside a 1 K environment in a high magnetic field. Further tensor polarization enhancement is achieved using additional RF saturation on the target magterial. Once enhanced, the nuclear polarization can be determined by analyzing the lineshape of the NMR absorption spectrum. This talk will describe the DNP system used at the University of New Hampshire, and explain novel techniques in inducing high tensor polarization in deuterium.
Tuesday, November 29th, 2022 3:30 PM PST (zoom)
Dr. Jochen Klein (CERN, zoom)
Host: Nu Xu
"Physics Program and Detector Development with ALICE3"
ALICE 3 constitutes the next-generation upgrade for heavy-ion physics in LHC Runs 5 and 6. It addresses the questions about the quark-gluon plasma which remain inaccessible to other existing or planned experiments, e.g. on the transport properties and thermalisation in the QGP, the formation of hadrons, and the early stages of the plasma evolution. To this end, precise measurements of heavy-flavour probes as well as of electromagnetic radiation are key. The required pointing and tracking performance are achieved with a high-resolution vertex tracker, installed within the beam pipe, and a large-acceptance tracker, both based on monolithic silicon-pixel sensors. The particle identification relies on a combination of a silicon-based time-of-flight detector and a Ring-Imaging Cherenkov detector. In addition, an electromagnetic calorimeter, a muon identifier, and a dedicated forward detector for ultra-soft photons are foreseen. In this presentation, we will explain the detector concept and its physics reach as well as discuss the innovative R&D activities in areas of interest for HEP experiments in general.
Tuesday, November 15th, 2022 10 am PDT (special time ) (zoom)
Dr. Tommaso Giani (NIKHEF Amsterdam)
Host: Shujie Li
"Evidence for Intrinsic Charm Quarks in the Proton"
It has been argued for a long time that the proton could have a sizable intrinsic component of the charm quark.
I will discuss how to disentangle the intrinsic charm component from charm-anticharm pairs arising from high-energy radiation and present results providing evidence for intrinsic charm, by exploiting the NNPDF4.0 high-precision determination of proton Parton Distribution Functions. The existence of intrinsic charm is estabilished at the 3σ level, with a momentum distribution in remarkable agreement with model predictions. Finally I will discuss how these findings are supported by the very recent data on Z-boson production with charm jets from the LHCb experiment.
Thursday, November 10th, 2022 3:30 PM PDT (in person & zoom)
Dr. Misha Stephanov (UIC)
Host: Nu Xu
"Predicting randomness in relativistic hydrodynamics"
We usually think of hydrodynamics as a deterministic description of fluid motion. The focus of this talk is on random fluctuations in fluids caused by thermal noise, inherent in systems with dissipation. The interest in this subject is driven by the progress of heavy-ion collision experiments towards the mapping of the QCD phase diagram. In particular, the search for the QCD critical point at RHIC requires quantitative understanding of fluctuations and their dynamics. I will discuss the role of the fluctuations in hydrodynamics and how we can predict their evolution using deterministic equations.
Photo credit: Jessica Rotkiewicz
Tuesday, November 8th, 2022, 3:30 PM PDT (Zoom only)
Dr. Björn Schenke (BNL)
Host: Farid Salazar
"QCD at the Crossroads: Hot QCD Town Hall meeting summary"
In this talk, I will try to summarize the discussions/presentations at the QCD town meeting, Boston, September 23-25: https://indico.mit.edu/event/538/.
Tuesday, November 1st, 2022, 3:30 PM PDT
In-person (Theory Lounge 70-228) & Zoom
Dr. Feng Yuan (LBNL)
Host: Nu Xu/Farid Salazar
"QCD at the Crossroads: Cold QCD Town Hall meeting summary"
In this talk, I will try to summarize the discussions/presentations at the QCD town meeting, Boston, September 23-25: https://indico.mit.edu/event/538/.
Tuesday, October 25, 2022, 3:30 PM PDT
In-person (Theory Lounge 70-228) & Zoom
Dr. Tyler Hague (LBNL)
Host: Shujie Li/Jennifer Rittenhouse West
"The EMC Effect: Light Nuclei are Weird"
In 1983, the European Muon Collaboration (EMC) recorded Deep-Inelastic Scattering data on Iron, Deuterium, and Hydrogen. Comparisons of the targets noted that the quark structure of nucleons is modified by the surrounding nuclear environment, dubbed the EMC Effect. Nearly 40 years later, the community is still working to understand the mechanism behind this. Initial studies of the EMC Effect on heavy nuclei were able to paint broad strokes pictures of how the effect scales across nuclei. However, later precision tests of light nuclei were found to be in tension with these previous understandings. Key missing pieces to understanding this are the free neutron structure function and nuclear effects. The MARATHON experiment used a novel technique to extract F2n/F2p by largely canceling nuclear effects in the A=3 mirror nuclei in the yield ratio. In this talk, I will give an overview of our current knowledge of the EMC Effect followed by a discussion of the MARATHON experimental results and recent work applying these to light nuclei to understand nuclear effects.
Thursday, October 20th, 2022 3:30 PM PDT
In-person (Theory Lounge 70-228) & Zoom
Mr. Henry Klest (Stony Brook University)
Host: Nu Xu
Host: Nu Xu
Teaching an Old Experiment New Tricks: Measuring Modern Jet Observables Using Archived H1 e+p DIS Data
Slides Youtube
A renaissance in jet physics is now underway, with novel, theoretically rigorous approaches to jet measurements being used to probe QCD in new ways using data from hadronic collisions at RHIC and the LHC. It is timely to explore these new techniques using data from high-energy collider experiments, which were recorded before these techniques were developed. In particular, colliders with leptons in the initial state provide a clean and complementary environment to study jets. The H1 experiment was a hermetic, general-purpose detector at the HERA electron-proton collider complex at DESY, which terminated data-taking in 2007. However, the H1 Collaboration continues to be active scientifically, preserving the data and updating analysis software. The H1 dataset therefore remains as accessible for high-quality analyses as that for currently running experiments, making it the ideal playground for testing modern QCD analysis approaches on DIS data before the EIC turns on. This talk will focus on the measurement of groomed event shapes in ep DIS collisions, using a set of novel inclusive observables which leverage recent advances such as the Centauro jet algorithm and precision jet grooming phenomenology. The advantages and challenges of the event-wide grooming technique will be discussed, as well as some lessons learned that are applicable to the EIC physics program.
Tuesday, October 18th, 2022, 3:30 PM PDT (in person & zoom)
Dr. Minjung Kim (UC Berkeley and LBNL)
Host: Nu Xu
Quarkonium Production in Heavy-ion Collisions at the LHC
Measurements of J/ψ production have been a valuable probe to study the properties of the hot and dense medium created in heavy-ion collisions, also known as the quark-gluon plasma (QGP). Experimentally, the first glimpse of the QGP was provided by collisions of lead beams at the Super Proton Synchrotron (SPS) in the late 90s via the measurements of J/ψ production. The suppression of J/ψ production in Pb–Pb collisions with respect to p–A collisions was observed, which was proposed as a smoking gun of the QGP as a consequence of colour screening in the QGP medium keeping charmed quark-antiquark pairs from binding to each other.
The higher collision energy at the Large Hadron Collider (LHC) with respect to previous collision programs at SPS and RHIC opened new perspectives on quarkonium measurements due to the increased heavy quark production cross section. The large data samples collected at the LHC based on the excellent performance of the LHC and the four experiments provided precise measurements of charmonium and bottomonium production in a wide kinematic range. Moreover, a multitude of new observables including multi-differential measurements of various quarkonium states becomes accessible, which provided crucial inputs to disentangle various quarkonium in-medium effects in the presence of the QGP.
In this talk, a selection of recent quarkonium measurements at the LHC will be discussed.
Tuesday, October 11th, 2022, 3:30 PM PDT (Zoom only)
Dr. Niklas Mueller (U. Washington)
Host: Farid Salazar
What can QIS do for high energy and nuclear physics?
The possibility to simulate quantum many-body systems with digital quantum computers and analog devices is an exciting opportunity for high energy and nuclear physics. I will present an overview over new directions in two old examples: understanding systems far-from-equilibrium, such as QCD in ultra-relativistic heavy ion collisions, and their approach to thermal equilibrium, and addressing thermal systems in regimes where Monte-Carlo importance sampling techniques face a sign problem. For those of you impatiently waiting for quantum computers to outrun classical computers, I will emphasize that QIS not only allows to make progress computationally, but more importantly conceptually, including previously unexplored aspects such as, e.g. entanglement. I will present a few relevant examples, still far from the ultimate goal QCD, but interesting because of their interdisciplinary relevance for high energy and nuclear physics, condensed matter theory and quantum information science.
Tuesday, October 4th, 2022, 3:30 PM PDT (Zoom only)
Dr. Yoshitaka Hatta (BNL)
Host: Farid Salazar
Spin Physics Opportunities at the EIC
Slides Youtube
I give an overview of high energy QCD spin physics with particular emphasis on physics opportunities at the future Electron-Ion Collider. Topics will include longitudinal spin decomposition, orbital angular momentum, spin at small-x, Ji sum rule and the generalized parton distributions, and transverse single spin asymmetries. I review the recent developments in the field and identify what are the outstanding challenges at the EIC.
Thursday, 08.11.2022, 2:30 PM PDT Special date and time! in the Theory Lounge (hybrid)
Dr. Raymond Ehlers (LBNL)
Host: Nicole Apadula/Peter Jacbos
What can we learn about the quark-gluon plasma from reconstructed jets with Bayesian inference?
Bayesian inference provides an approach for constraining the parameters of complex models according to the available information. In particular, the wealth of information contained within multi-messenger experimental measurements provides the opportunity for detailed data-model comparison. The need for such rigorous comparison is pervasive throughout science. The JETSCAPE collaboration has now applied this Bayesian approach to the familiar problem of jet quenching. In this talk, I will discuss our recent results, in-progress analysis, and implications for the future of the field.
Wednesday, 06.29.2022, 3:30 PM PDT
Joint Nuclear Theory/HIT seminar! Special date on Wednesday!
Dr. Jennifer Rittenhouse West (LBNL)
Host: Xin-Nian Wang
Diquark Formation as a Breakthrough of Fundamental QCD into Nuclear Physics
A diquark bond formed from valence quarks across a nucleon-nucleon pair has been proposed as the fundamental quantum chromodynamics (QCD) physics causing short-range correlations (SRC) in nuclei. Short-range correlated nucleon-nucleon pairs and the nucleon shell model are the basis for nuclear physics, with SRC accounting for 20% of the nucleons in a nucleus. While SRC have been extensively studied both experimentally and theoretically, notably by the CLAS collaboration in recent years, their underlying cause at the QCD level has remained a mystery. The diquark formation model, if shown to be the cause of SRC in nuclei, represents a breakdown of the assumption of scale separation in effective field theories. Rather than a boundary between scales, however fuzzy and broad, a case is made in this work for diquark formation as a direct breakthrough of the underlying theory, capturing 20% of the physics of nuclear structure.
Tuesday, 06.21.2022, 3:30 PM PDT
Dr. Aihong Tang (BNL)
Host: Xin-Nian Wang
Global Spin Alignment in Relativistic Heavy Ion Collisions : A Progress Review
In relativistic heavy ion collisions, quarks can possess global spin polarization in a globally vortical system. Such process is initially induced by the spin-orbital coupling, and the evolution of polarized quarks and the subsequent formation of hadrons involves various interesting physics mechanisms. This phenomena can be studied either by global spin polarization of hyperons or global spin alignment of vector mesons. Recently the STAR collaboration released interesting results of global spin alignment for phi- and K*-mesons. It is found that the surprisingly large value of phi-meson global spin alignment cannot be explained by conventional mechanisms, but can be accommodated by a model invoking the strong force field. In this talk we will review the recent progress in the understanding of global spin alignment, and in particular we will discuss STAR's result and its implications.
Monday, 06.13.2022, 3:00 PM PDT (Hybrid at Persevervance Hall, note special time and date!)
Prof. Ulrich Mosel (Giessen University)
Host: Jennifer Rittenhouse West
Neutrino-nucleus interactions in quantum-kinetic transport theory
The analysis of results from long-baseline experiments such as T2K, NOvA and DUNE requires knowledge of the incoming neutrino energy. The latter has to be reconstructed from only partially measured final states of the reaction. Any theory thus has to go beyond the calculation of inclusive cross sections and has to deliver the full final state of the reaction. Since all present experiments work with nuclear targets not only the initial, first interaction of the incoming neutrino plays a role. In addition, the final state interactions of the initially produced hadrons with the nuclear environment are important and determine the final state. The state-of-the-art method to treat such processes is quantum-kinetic transport theory which has been around since 50 years, but only over the last 20 years major numerical implementations to describe nuclear reactions have become available. In my talk I will illustrate some of the results obtained with such a theory, applied both to nuclear reactions and neutrino-nucleus reactions.
Tuesday, 06.07.2022, 12 PM PDT - Special time!
Dr. Sergey Kulagin (Institute of Nuclear Research, RAS Moscow)
Host: Jennifer Rittenhouse West
What can we say about modification of the bound nucleon at the parton level from global QCD fits?
We briefly review available experimental observations on nuclear effects in deep-inelastic scattering (DIS). We then briefly discuss a few basic mechanisms responsible for nuclear corrections and review progress in understanding the observed phenomenon focusing on the valence quark region. We report the results of our global QCD analysis which includes a "standard" set of high-energy data for the proton target (DIS, DY production of lepton pair as well as W+- / Z boson production) and also nuclear 2H, 3H, and 3He DIS data. In this analysis we treat nuclear corrections in DIS in terms of a nuclear convolution approach with off-shell bound nucleon. The off-shell correction describes the modification of parton distributions in bound nucleons, which is determined along with the parton distribution functions (PDFs). A number of systematic studies have been performed aiming to estimate the uncertainties arising from the use of various deuterium data sets, from the model of high twist contributions to the structure functions, from the treatment of target mass corrections. We compare our predictions for the ratio F2n/F2p and the d/u ratio of the quark distributions with the results of other analyses as well as with the recent data from the MARATHON experiment.
Tuesday, 05.31.2022, 3:30 PM PDT
Dr. Christopher McGinn (Univ of Colorado Boulder)
Host: Sooraj Radhakrishnannan
Inclusive and Electroweak Boson-tagged Jets as Probes of the Quark-Gluon Plasma and Medium Response
Jets, as proxy for hard scattered partons in initial collision of heavy and ultrarelativistic nuclei, are modified significantly relative their vacuum reference counterparts when traversing the subsequently formed hot-and-dense medium of deconfined quarks and gluons known as the Quark-Gluon Plasma (QGP). Specifically, a suppression in the overall production of jets is observed compared to vacuum expectation, as well as a modification to jet fragmentation patterns towards softer fragments. These phenomena are known collectively as 'jet-quenching'. Recently, much attention has been paid to the impact of jet-medium interactions on the medium itself, in searches for medium response and in searches for quenching in small systems (such as proton-nucleus collisions) in the context of observed high-pT v2. Using data taken with the ATLAS detector at the LHC, sqrt(sNN) = 5.02 TeV, jets produced with electroweak boson partners (unmodified by strong-force interactions in QGP) are studied to characterize both the jet production and fragmentation, with the latter providing insight into the necessity of incorporating medium response in theoretical model comparisons. Additionally, simultaneous studies of jet v2 and quenching in big-and-small systems reveals there may be more questions on the exact nature of the jet-medium interactions in both systems and how they lead to the physical final state observed.
Tuesday, 05/24/2022,3:30 PM PDT
Prof. Mike Lisa (Ohio State University)
Host: Xin-Nian Wang
Subatomic Smoke Rings: Polarization and Toroidal Vorticity in the QGP
Since the discovery of global hyperon polarization in Au+Au collisions at RHIC about five years ago, there has been intense theoretical and experimental focus on the topic. After a brief review, I will discuss novel vortex structures that may be generated in two situations. The first is a p+A collision, which may produce droplets of QGP that develop toroidal vortex ("smoke ring") structure. Experimental observation of such a structure would provide compelling evidence supporting the hydrodynamic nature of this tiny system, a much-debated topic today. The other is an idealized "hot moving spot" that may result from thermalization of a jet in an expanding QGP; in this case, the "smoke ring" centers on the jet direction. In both cases, we suggest an experimental observable to measure the toroidal vortex structure, and present full hydrodynamical simulations to make quantitative predictions, including initial state fluctuation effects. I will mention prospects and challenges for observing this novel phenomenon in experiment.
Tuesday, 05.17.2022, 3:30 PM PDT
Prof. Jorge Noronha (UIUC)
Host: Xin-Nian Wang
Hydrodynamic Frames: the Good, the Bad, and the Ugly
Three of the most cutting-edge experiments in modern science, RHIC, LHC, and LIGO are now producing data whose description requires a major overhaul of our current understanding of what constitutes fluid dynamic behavior in the relativistic regime. In this talk I will explain how the choice of hydrodynamic variables in a system out of equilibrium, i.e., our definition of the so-called hydrodynamic frame, affects the domain of applicability of relativistic viscous fluid dynamics formulations. I will also show how developments in relativistic viscous hydrodynamics obtained in heavy-ion collisions could be instrumental in determining the viscous properties of ultradense matter formed in neutron star mergers.
Tuesday, 05.10.2022, 3:30 PM PDT
Prof. Kenji Fukushima (Univ. of Tokyo)
Host: Feng Yuan
Continuity or Discontinuity between Nuclear and Quark Matter and the Astrophysical Implications
In this talk I will review theoretical scenarios of quark matter at high density. Although a phase transition is not logically excluded, a crossover or weak first-order transition is likely to occur. I will explain how the equation of state is constrained by the neutron star observation and demonstrate that the future gravitational wave detection can identify the nature of the quatk matter onset.
Wednesday, 05.04.2022, 3:30 PM PDT (Special date)
(Hybrid talk in the INPA room)
Prof. Carl Schroeder (LBNL/UCB)
Host: Peter Jacobs
Laser-Plasma Accelerators
Laser-driven plasma-based accelerators (LPAs) are able to sustain extremely large accelerating gradients, orders of magnitude larger than those achievable using conventional metallic accelerating structures. LPA experiments have demonstrated the generation of multi-GeV electron beams in cm-scale plasmas. These high gradients have attracted interest in LPA technology for high-energy collider applications. In this talk, I will review the basic physics of LPAs, LPA research in the BELLA Center at LBNL, and how LPAs can be developed for various applications. Employing LPAs as a linac for an e+e- collider is the most challenging application, and I will discuss the design considerations and expected performance for an LPA-based linear collider. .
Tuesday, 04.26.2022, 3:30 PM PDT
(This will be a hybrid seminar in theTheory Lounge)
Dr. Jan Steinheimer (FIAS)
Host: Sooraj Radhakrishnan
Hyper-nuclei production in heavy-on collisions
Hypernuclei have been an interesting topic of study for more than half a century. Yet their properties are still not fully understood. In this talk, I will give a short introduction to hypernuclei and how they can be produced. Here, the production of nuclei with one or more units of strangeness from relativistic heavy ion collisions is of particular interest, due to the abundance of strange baryons created. While the absorption of hyperons offers a chance to create large hypercluster in the spectator fragments of nuclear collisions, also the observation of light hypernuclei from the central hot region is of interest. I will discuss how the production probability can be well described by a coalescence mechanism using the UrQMD model over a beam energy range of three orders of magnitude. In addition I will show how the measurement of different nuclei can be used to determine the size of the region of homogeneity from which baryons, that will eventually form (hyper-)nuclei, are emitted . Within this context I will discuss recent interpretations of the centrality dependence of (hyper-)nuclei production.
Quark and Gluon Spatial Distributions in the Nucleon
Studying the role of gluonic observables in exclusive scattering processes is essential as new physics programs, such as an electron ion collider, are planned in unprecedented kinematic regimes. I will present a parameterization of quark and gluon generalized parton distributions (GPDs) calculated using a reggeized spectator model. This parameterization is constrained using a combination of lattice QCD form factor calculations and extracted deep inelastic parton distributions. We evolve our parameterization at leading order in Q2 to the scale of experimental data using a perturbative QCD evolution framework. We demonstrate expected spatial distributions under Fourier transformation using our parametrization. Understanding the behavior of gluon GPDs is a first step towards extracting the gluon contribution to deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) observables at the EIC.
Tuesday, 04.12.2022, 3:30 PM PDT
Dr. Gunther M Roland (MIT)
Host: Sooraj Radhakrishnan
Hot QCD with sPHENIX at RHIC
Over the last decades heavy-ion experiments at RHIC and LHC have demonstrated a range of novel QCD phenomena that emerge under conditions of extreme pressure and temperature. New efforts, sPHENIX at RHIC and the upgraded LHC experiments, will begin collecting high precision new data in the next year. These data will allow us to investigate the microscopic origins of observed phenomena in the produced Quark-Gluon Plasma (QGP). Of particular importance will be the complementarity of experiments in the two energy regimes, elucidating the temperature dependence of QGP properties. In this talk I will present the sPHENIX design, construction status and expected performance, and discuss case studies that illustrate key aspects of the sPHENIX physics program.
Tuesday, 03.29.2022, 3:30 PM PST
Prof. MaElena Tejeda Yeomans (Universidad de Colima)
Host: Jennifer Rittenhouse West
Rise and Fall of Lambda and anti-Lambda Polarization from the Core-Corona Model
The polarization of particles produced in heavy-ion collisions provides the perfect arena to study amazing phenomena such as the collective rotation of the nuclear medium, the transference of global angular momenta to spin properties of certain particles, and the evolution of these properties when there are drastic changes in the properties of the hot and dense medium. Recently, measurements by STAR collaboration at RHIC and HADES collaboration at GSI show the rising of Lambda and anti-Lambda global polarization with decreasing collision energy. Many models predict the vanishing of global polarization due to the lack of system angular momentum, but the height and location of the expected peaks for both Lambda and anti-Lambda are still not well understood. In this talk I will report on recent work to study Lambda and anti-Lambda global polarization in heavy-ion collisions using the core-corona model, where the source of these hyperons is a high-density core and a less dense corona. I will show that the overall properties of the polarization excitation functions can be linked to the relative abundance of Lambdas and anti-Lambdas coming from the core versus those coming from the corona. We will see how the global polarization peak at the expected ranges of collision energies but, the exact positions and heights of these peaks depend on the centrality class, which is directly related to the QGP volume and lifetime, as well as on the relative abundances of Lambdas and anti-Lambdas in the core and corona regions. Finally, I will talk about the improvements we are making to this model to study polarization properties of other species, and as a probe of critical phenomena in the nuclear medium.
Tuesday, 03.22.2022, 3:30 PM PST
Dr. Xiaojun Yao (MIT)
Host: Xin-Nian Wang
Pure quark and gluon jet observables
Disentangling quark- and gluon-initiated jets can help us to better understand fundamental interactions in QCD and use jets as probes of the quark-gluon plasma in heavy ion collisions. Many previous studies relied on the Sudakov factors of some jet substructure observables such as the soft drop jet mass in the tail region and failed to reach a 100% efficiency in the disentangling. In this talk, I will introduce novel jet observables that are made pure quark or gluon in a wide kinematic region. The construction is based on the collinear drop grooming technique and nonperturbative effects are taken into account. I will show both analytic and Monte Carlo results for these observables in proton-proton collisions and discuss the impact of initial-state radiation and multi-parton interaction. Finally, I will discuss the potential obstacles in applying these observables in heavy ion collisions.
Tuesday, 03.15.2022, 2:00 PM PST (Special time)
Dr. You Zhou (NBI)
Host: Xin-Nian Wang
Multi-particle correlations for the new decade of QGP studies
Multi-particle correlations have been compelling tools to probe the properties of the Quark-Gluon Plasma (QGP) created in the ultra-relativistic heavy-ion collisions. In this seminar, I will present a generic recursive algorithm for multi-particle cumulants, which enables the calculation of arbitrary order multi-particle cumulants. Among them, I will emphasize a particular series of mixed harmonic multi-particle cumulants, which measures the general correlations between any moments of different flow coefficients. The study of these new multi-particle cumulants in heavy-ion collisions will significantly improve the understanding of the initial event-by-event geometry fluctuations and the hydrodynamic response in the final state. This will pave the way for more stringent constraints on the initial state and help extract more precise information on how the created hot and dense matter evolves. Last but not least, I will show the most recent study of correlations between anisotropic flow and mean transverse momentum in terms of multi-particle correlations/cumulants. I will show how we can directly access the initial conditions of heavy-ion collisions using the latest experimental measurements at the LHC and discuss the critical challenge of the state-of-the-art QGP studies via Bayesian analyses.
Tuesday, 03.08.2022, 2:00 PM PST
Dr. Giuliano Giacalone (Heidelberg University)
Host: Xin-Nian Wang
The initial state of the quark-gluon plasma: status, prospects, interdisciplinary connections
The hydrodynamic model of the quark-gluon plasma (QGP) formed in relativistic nuclear collisions has permitted us over the years not only to obtain quantitative estimates of the transport properties of this medium from data, but also to establish a phenomenologically viable picture of its initial condition and how it emerges from the interaction of two ions at high energy. I review the current understanding of the initial condition of the QGP, emphasizing the outcome of state-of-the-art models and the overall picture that they yield. I discuss the progress made in the definition of observable quantities that offer a specific sensitivity to the physics of the initial state, with a focus on recent results (both theoretical and experimental) on mean transverse momentum-anisotropic flow correlations. Such observables pose unprecedented constraints on the parameters of state-of-the-art Monte Carlo generators for nuclear collisions, demonstrating, in particular, the importance of having an accurate implementation of the structure of the colliding ions, and the nucleons therein, in such frameworks. Consequently, the initial state of heavy-ion collisions provides fertile ground for new interdisciplinary connections involving different aspects of hadronic and nuclear physics across energy scales.
Tuesday, 2022.02.22, 3:30 PM PST
Yi Yin (Quark Matter Research Center, Institute of Modern Physics (Chinese Academy of Science))
Host: Sooraj Radhakrishnan
Spin-momentum correlation in hot and dense QCD matter
The transport phenomena involving spin are instrumental in investigating quantum effects in many-body systems. In heavy-ion collisions, the recent measurement of spin polarization and spin alignment opens a new avenue to explore the properties of hot and dense QCD matter. Based on linear response theory and quantum kinetic equation, we have systematically studied spin-momentum correlation induced by hydrodynamic gradients [1]. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear [2]. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. The possible signature of SIP at RHIC and LHC will be elaborated. Then, I will present our prediction for the signature Spin Hall effect induced by baryon chemical gradient at RHIC beam scan energies [3,4]. If time permitted, I will briefly discuss the effect of SIP on vector mesons. .
Wednesday, 2022.02.015, 3:30 PM PST
Douglas Higinbotham (Jefferson Lab)
Host: Jennifer Rittenhouse West
The End of the Proton Radius Puzzle?
For many years scientists believed that the proton radius was 0.877(6) fm based on a series of atomic Lamb shift and electron scattering measurements. In 2010, a new type of measurement, making use of muonic hydrogen, determined the radius to be 0.842(1) fm. The large systematic difference between muonic hydrogen measurements and the previous results became known as the proton radius puzzle. To solve this puzzle, a world-wide theoretical and experimental investigation has been undertaken. I will review the status of the puzzle with an emphasis on electron scattering results and the systematic differences between the different analysis techniques that led to disparate conclusions. I will leave it to the audience to decide if the puzzle is solved.
Joint NT and HIT seminar (note special day and time)
Wednesday, 2022.02.02, 1:00 PM PST
Dr. Yong Zhao (Argonne National Lab)
Host: Aaron Meyer
Lattice QCD Determination of the Bjorken-$x$ Dependence of PDFs at Next-to-next-to-leading Order
The large-momentum effective theory (LaMET) is a systematic approach to calculate parton physics from Euclidean approaches such as lattice QCD. With major progress in the lattice renormalization and perturbative matching, the lattice calculation of PDFs with LaMET is now entering the stage of precision control. In this talk, I will present a state-of-the-art lattice QCD calculation of pion valence quark distribution with next-to-next-to-leading order matching correction, which is done using two fine lattices with spacings $a=0.04$ fm and $0.06$ fm and valence pion mass $m_\pi=300$ MeV at boost momentum as large as 2.42 GeV. I will demonstrate that perturbative matching in Bjorken-$x$ space yields a reliable determination of the valence quark distribution for moderate x with a target precision, which shows considerably improved systematic uncertainty compared to a previous analysis of the same lattice data with a short-distance factorization approach in the coordinate space, and is in excellent agreement with the most recent global analyses.
Tuesday, 2022.01.25, 3:30 PM PST
Prof. Rene Bellwied (University of Houston)
Host: Sooraj Radhakrishnan
Matter under extreme conditions - Particle Collisions along the QCD Phase Diagram
Relativistic particle collisions have come a long way during the past two decades with the characterization of states of matter along the QCD phase transition line. I will try to show how these discoveries lead to significant multi-disciplinary efforts to understand the creation and evolution of matter under extreme conditions. Examples that will be highlighted are the connection of fundamental quantum theories to collective phenomena and particle production, as well as astrophysical measurements that link to interactions observed at RHIC and LHC.
Tuesday, 2022.01.18, 3:30 PM PST
Prof. Tanja Horn (JLab & The Catholic University of America)
Host: Jennifer Rittenhouse West
PION AND KAON STRUCTURE FUNCTIONS
Slides Youtube
Pions and kaons are, along with protons and neutrons, the main building blocks of nuclear matter. They are connected to the Goldstone modes of dynamical chiral symmetry breaking, and appear to be key to the further understanding of the mechanisms that generate all hadron mass in the visible universe. The distribution of the fundamental constituents, the quarks and gluons, is expected to be different in pions, kaons, and nucleons. However, experimental data are sparse. As a result, there has been persistent doubt about the behavior of the pion's valence quark structure function at large Bjorken-x and virtually nothing is known about the contribution of gluons. Experiments at the 12 GeV JLab using hard scattering from the virtual meson of the nucleon will shed light on this by providing information on how emergent mass manifests in the wave function and about the quark-gluon momentum fractions. The Electron-Ion Collider (EIC) with an acceptance optimized for forward physics will enable a revolution in our ability to study pion and kaon structure. The unique experimental facilities at the EIC will provide access to structure functions over a wide range of kinematics. This would allow for measurements testing if the origin of mass is encoded in the differences of gluons in pions, kaons, and nucleons, and measurements that could serve as a test of assumptions used in the extraction of structure functions and the pion and kaon form factors. Measurements at an EIC would also allow to explore the effect of gluons at high x. In this talk we will discuss the status of measurements at Jefferson Lab and prospects of such measurements at the EIC.
Tuesday, 2022.01.11, 3:30 PM PST
Prof. Jiangyong Jia (SUNY Stony Brook)
Imaging nuclear structure in heavy-ion collisions
The hydrodynamic modeling of the quark-gluon plasma (QGP) permits us today not only to perform quantitative extractions of the transport properties of the QGP, but also to strongly constrain its initial condition. A growing body of experimental evidence shows that the QGP initial condition is strongly impacted by the shape and radial structure of the colliding nuclei. We discuss the exciting prospect of using precision flow measurements as a tool to image the structure of atomic nuclei, and show how such measurements probe the quadrupole, octupole, and triaxial deformations of the colliding ions, as well as their neutron skin. Motivated by recent groundbreaking measurements from RHIC and LHC, we discuss in particular the case of collisions of isobaric nuclei, which provide the cleanest access route to the collective structure of the colliding ions. We discuss the implications of obtaining an information about the structure of nuclei from high-energy collisions that is fully complementary to that obtained in low-energy experiments, and argue that a scan of stable isobars at high-energy colliders may open a new exciting direction of research in nuclear physics.