Previous HIT Seminars

March 25 2025 (in-person)

Provakar Datta ( LBNL)

Host: John Arrington

Slides  YouTube 

Title:Unveiling the Neutron’s Electromagnetic Structure: Preliminary Results from SBS-GMn Experiment

Abstract:  The nucleon electromagnetic form factors (EMFFs) are fundamental observables that provide insight into the nucleon's internal structure. However, aside from the proton's magnetic form factor GMp, high-precision data for the nucleon EMFFs at high momentum transfer (Q^2) remain scarce due to the experimental challenges associated with such measurements. 

To address this, the Super BigBite Spectrometer (SBS) collaboration is conducting a series of experiments in Jefferson Lab's Hall A to extend high-precision measurements of the remaining nucleon EMFFs up to or beyond Q^2 =10 (GeV/c)^2 , significantly improving the current situation. The first of these experiments, SBS-GMn, was conducted from October 2021 to February 2022 with the goal of extending measurements of the neutron magnetic form factor GMn in the Q 2 range of 6 to 13.5 (GeV/c)^2 using the “ratio” method. This approach minimizes systematic uncertainties by extracting GMn from the ratio of neutron-coincident (D(e,e'n)) to proton-coincident (D(e,e'p)) quasi-elastic electron scattering from deuterium.

In this talk, I will provide an overview of the SBS-GMn experiment, discuss the physics analysis methodology, underlying challenges, and present preliminary results. I will also explore the implications of these results for the flavor decomposition of nucleon form factors into up- and down-quark contributions.

March 11 2025 (in-person)

Volodymyr Y. Vovchenko ( University of Houston)

Host: Volker Koch

Slides  YouTube 

Title: Fluctuation Probes of QCD Matter in Heavy-Ion Collisions

Abstract:  This talk explores fluctuation probes of QCD matter generated in heavy-ion collisions at RHIC and LHC. First, the RHIC-BES-II data on proton cumulants is examined within the framework of hydrodynamic calculations and in the context of QCD critical point expectations.  We elaborate on the properties of appropriately scaled factorial cumulants and how acceptance dependence analysis can illuminate the presence of short- and long-range correlations.  Challenges in simultaneously describing protons and antiprotons will be emphasized, highlighting what the differences between the two can reveal about the thermalization of the system.  In the second part of the talk, the topic of net-charge fluctuations as an indicator of fractional quark charges will be revisited.  Utilizing a novel approach for describing 2-point charge density correlations, we perform a quantitative analysis of LHC measurements, which reveals moderate evidence for the freeze-out of charge fluctuations taking place in the QGP.

March 4 2025 (in-person)

Thomas Richardson (LBNL)

Host: Andre Walker-Loud

Slides  YouTube 

Title: Two-baryon interactions and currents from large-Nc QC

Abstract:  The large-Nc limit of QCD leads to an emergent spin-flavor symmetry in the baryon sector. This symmetry explains several properties such as the ratios of masses, magnetic moments, and meson couplings. It also provides an explanation of the relative sizes of couplings in phenomenological two-nucleon potentials. We discuss recent applications of the spin-flavor symmetry in large-N QCD to nuclear forces and currents relevant for beyond the Standard Model searches including neutrinoless double beta decay and CP violation. We also discuss new symmetries that emerge in the unitary limit for two-baryon scattering.

February 25 2025 (in-person)

Ben Gilbert (Livermore)

Host: Spencer Klein

Slides  YouTube 

Title: Measurement of photonuclear dijet production in ultra-peripheral Pb+Pb collisions at the LHC with the ATLAS Detector

Abstract:  In ultra-relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Photon-induced processes are the dominant interaction mechanism when the colliding nuclei have an impact parameter larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus, analogous to deep inelastic scattering. This talk presents a measurement of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, rapidity gaps, and forward neutron emission to identify inclusive photo-nuclear hard-scattering processes. These measurements also include detailed studies of rapidity gap distributions and nuclear break-up effects, allowing for precise comparisons between data and theory for inclusive photo-nuclear processes. The measured cross-sections are compared to theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not well constrained by world data, demonstrating the potential of these data to provide a strong new constraint on nPDF effects.

February 18 2025 (in-person)

Ananya Rai (Yale University)

Host:  Barbara Jacak

Title: Probing QCD with projected N-Point Energy Correlators

Abstract: Jet substructure accesses the radiation history of a jet, providing a powerful tool for probing QCD across energy scales. In ultrarelativistic heavy-ion collisions, it helps investigate the microscopic properties of the Quark-Gluon Plasma (QGP). My research aims to answer the question “Can we systematically explore QCD energy scales to understand the emergence of various physical phenomena?” The projected N-Point Energy Correlators (ENCs) have emerged as a novel tool for probing hadronic collisions, offering a way to address this question. They are defined as energy-weighted correlations as a function of the largest angle between N particles. Jet evolution is imprinted in the slopes of the ENCs and they exhibit a distinct scaling behavior from perturbative to non-perturbative QCD. Moreover, ratios of higher-point correlators to the two-point correlator (ENC/E2C) provide insight into quantum scaling (anomalous dimensions), which is proportional to the strong coupling constant, αS. In this talk, I will present the measurement of the E2C, E3C, and the E3C/E2C ratio in proton-proton collisions at 13 TeV with the ALICE detector, highlighting their sensitivity to the running of αS. I will also discuss plans to extract αS from these measurements. Additionally, using the Hybrid Model, I showed that the E3C/E2C could be altered in the QGP due to the presence of jet wakes—soft hadrons produced when a traversing jet interacts with the strongly coupled QGP medium. This result has motivated the measurement of this ratio in ALICE Run 2 Pb-Pb data at 5.02 TeV, and I will discuss the ongoing work towards this goal. Finally, I will conclude by outlining prospective substructure measurements that will leverage the high-statistics data from Run 3 at the LHC. As we enter the era of jet tomography, these measurements will enable precise exploration of the microscopic properties of the QGP.

February 11 2025 (in-person)

Nathaly Santiesteban (University of New Hampshire - Durham)

Slides  YouTube 

Host:  John Arrington

Title:Exploring the Electromagnetic Form Factors of Protons and Neutrons: Current Understanding and Challenges

Abstract: The electromagnetic form factors of protons and neutrons contain critical information about the spatial distributions of their charge and magnetization. While extensive studies of electron-proton scattering using hydrogen targets have employed techniques such as Rosenbluth, Super-Rosenbluth, and polarization methods, discrepancies in the results are frequently attributed to the neglected two-photon exchange (TPE) effects. In contrast, the absence of a free neutron target complicates the study of neutron form factors. Several experiments have attempted to extract the neutron form factors through scattering off the neutron in deuterium, but the results often exhibit significant variation and are associated with substantial systematic uncertainties.

In this talk, I will present how using the Super-Rosenbluth technique with electron and positron beams can help us understand the discrepancies in proton measurements. Additionally, I will discuss the impact of recent quasielastic scattering results from mirror nuclei, such as ³H and ³He, on global parametrizations of the neutron magnetic form factor, offering new insights into its extraction.

February 04 2025 (in-person)

Vassu Doomra (Stony Brook University)

Slides  YouTube 

Host:  Barbara Jacak

Title: From Photons to Parity: Developing High-Precision Tracking Across Two Distinct Frontiers of Nuclear Physics

Abstract: This talk highlights the development of advanced tracking techniques applied across diverse environments, from precision electron scattering to explore physics beyond the Standard Model with the MOLLER experiment at Jefferson Lab to complex heavy-ion collisions for studying the properties of the partonic matter with the PHENIX experiment at BNL.

In the first part, we will present the first PHENIX measurement of disentangling lepton pairs into heavy-flavor decays, prompt pairs, and background pairs using the distance of closest approach (DCA) to the interaction point using p+p data at 200 GeV taken in 2015. The DCA calculation is enabled by the PHENIX Silicon Vertex Tracker (VTX), which, with a total radiation length of 15%, introduces a significant photon conversion background. We will highlight how recent improvements in tracking techniques have enabled the development of effective conversion rejection methods that significantly suppress these backgrounds, enhancing the signal-to-background ratio by orders of magnitude. The resulting heavy-flavor contributions to the e+e− pair spectrum and its implications will be discussed.

Next, we will shift to the MOLLER experiment, expected to run in 2026/27, where precise tracking is essential to accurately measure the parity-violating asymmetry (APV) in longitudinally polarized e-e scattering using the 11 GeV electron beam of the CEBAF at Jefferson Lab. Achieving the desired level of accuracy is based primarily on our ability to precisely calculate the average kinematic factor and validate the acceptance of the toroidal spectrometer system. To meet these challenges, we have developed a sophisticated track reconstruction algorithm, which will be the focus of the second part of the talk.

January 28 2025 (in-person)

Youqi Song (Yale University)

Host:  Barbara Jacak

Title: Studying non-perturbative QCD with jet substructure measurements at colliders

Abstract: Understanding non-perturbative QCD effects is important for comprehension of QCD dynamics. To study the non-perturbative regime in detail, I have led two sets of jet substructure measurements in pp collisions at 200 GeV at STAR. In this talk, I will present results from these studies.

• Measurements of the correlation between CollinearDrop and SoftDrop observables provide access to study the interplay between different components of the parton shower. CollinearDrop observables are sensitive to early-stage soft radiation, while SoftDrop observables are sensitive to later-stage hard splittings. The results are fully corrected with a simultaneous unfolding of six observables utilizing MultiFold, a novel machine-learning based unfolding algorithm, which preserves the correlations in the multi-dimensional observable phase space.

• Measurement of the charge-correlator ratio (rc) can shed light on hadronization mechanisms. rc can probe for the contribution of string-like fragmentation by distinguishing the charge signs of leading and subleading charged particles within jets. The result shows that common Monte Carlo models over-predict such correlation in data.

Finally, I will discuss future opportunities for jet substructure measurements at RHIC and the LHC, and how they could further our understanding of QCD.

January 21 2025 (online)

Mi Ke (CCNU)

Slides  YouTube 

Host: Nu Xu

Title: Recent Results on Baryon Correlations at RHIC-STAR

Abstract: In high-energy nuclear collisions, the measurements of two-particle femtoscopy is a powerful and unique method for extracting information about the femtoscopic spatio-temporal properties of the source and characterising the final state interactions (FSI). However, measurements of baryon correlations are scarce. Understanding the strong interactions between baryons, especially nucleon-nucleon (N-N), hyperon-nucleon (Y-N) and hyperon-hyperon (Y-Y) interactions, are crucial for comprehending the equation-of-state (EoS) of the nuclear matter and inner structure of neutron star. Furthermore, baryon correlations involving light nuclei, which are loosely bound objects, are critical for understanding many-body interactions and the production mechanisms of light nuclei.

    In this talk, we will present recent results on baryon correlations measured with RHIC-STAR experiment, including p-p,  p-d, d-d, p-\Lambda, p-Xi^-, and d-\Lambda. Extracted source size parameters, driven by collision dynamics, and FSI parameterization, determined by the nature of the particle pairs under study, will be discussed within the framework of lattice calculations (interaction potentials) and hadronic transport model calculations.

December 17 2024 (in-person)

Chen, Yi (Luna) (Vanderbilt University)

Slides  YouTube 

Host: Peter Jacobs

Title: Evidence of the medium response to hard probes with Z-hadron correlations in PbPb and pp collisions

Abstract: In ultrarelativistic heavy-ion collisions at RHIC and LHC, a new state of matter known as the quark-gluon plasma (QGP) is believed to be created. As high-energy quarks or gluons traverse the plasma, their interactions with the QGP reduce their energy while simultaneously injecting energy into the QGP, which then propagates. This interaction and energy propagation result in intriguing phenomena, including the diffusion wake, observed in several phenomenological models.

In this seminar, I will present a recent measurement from the CMS collaboration that successfully isolates some of these wake effects for the first time. The measurement analyzes the charged hadron distribution in azimuthal angle and pseudorapidity associated with a Z boson in PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS experiment. A stronger modification of charged hadron distributions near the Z boson is observed in PbPb collisions compared to the pp reference. This result provides new insights into the interactions within the QGP and contributes to a deeper understanding of the jet quenching phenomenon.

December 10 2024 (in person)

Kenneth Scott Mcelvain (Berkeley University & LBNL)

Slides  YouTube 

Host: Andre Walker-Loud

Title: Adiabatic Quantum Computation with the Fermionic Position Space Schrödinger Equation

Abstract:  I describe an efficient encoding of the fermionic Schrödinger equation in first quantization as a spin system Hamiltonian.   The challenging part of the construction is the implementation of the kinetic energy operator, which is essentially the Laplacian. The finite difference implementation on the lattice combines contributions from neighboring lattice sites, which is complicated by fermionic exchange symmetry.

November 26 (in-person)

Miguel Arratia (UC Riverside) 

Slides  YouTube 

Host: John Arrington

Title: Spin Alignment of Quarks In the Nucleus 

Abstract: I will describe upcoming measurements with the CLAS12 detector at JLab, which aim to provide the first measurements of nuclear effects on the spin structure of bound protons — a completely unexplored area. These measurements will use a longitudinally polarized lithium-7 target and an 11 GeV polarized electron beam. I will discuss the physics motivations and the expected performance of the experiment for both inclusive and semi-inclusive scattering. Additionally, I will outline how these measurements could inform future upgrades for the EIC. I will also describe planned measurements of Lambda particles using the ePIC Zero-degree calorimeter. Lambda studies will be a unique tool, including for merging spin-related studies with studies of cold nuclear matter at the EIC.

November 21 (in-person)

David d'Enterria (CERN) 

Slides  YouTube 

Host: Spencer Klein

Title: Photon-photon physics at the LHC 

Abstract: The CERN LHC is not only the current energy-frontier collider for parton-parton collisions, but has proven a powerful photon collider providing photon-photon (γγ) collisions at center-of-mass energies and luminosities never reached before. By exploiting the large fluxes of quasireal photons emitted by the accelerated protons and heavy-ions, a very rich and unique range of SM and BSM measurements is open to study. Such γγ processes can be examined in particularly clean conditions in the so-called ultraperipheral collisions (UPCs) where the colliding hadrons interact without hadronic overlap, and survive their purely electromagnetic interaction. I will review the latest experimental and theoretical photon-photon physics results at the LHC including measurement of the anomalous tau lepton magnetic moment via γγ->tau+tau- production, observation of light-by-light scattering, and searches for axion- and graviton-like particles, among others. 

November 12 (in person)

Xoán Mayo López (University of Santiago de Compostela)

Slides  YouTube 

Host: Wenbin Zhao

Title: The imprints of the medium evolution in jet quenching

Abstract:  In this talk, we present a novel extension to the theory of jet quenching, incorporating the effect of both the flow and anisotropy of matter undergoing hydrodynamic evolution. First, we study the modifications to the gluon radiation spectra in the pressence of evolving matter, which becomes anisotropic in the transverse plane to the jet propagation. Second, we annalyze the interplay between the two, which results in a significant rescaling of fundamental objects like the energy loss rate and jet quenching parameter, potentially transforming our understanding of jet-medium interactions drastically. Finally, we discuss phenomenological implications that the presented results have for a realistic imaging of the QGP created in HICs.

November 05 (in person)

Tom Reichert (Frankfurt Institute for Advanced Studies (FIAS))

Slides  YouTube 

Host: Volker Koch

Title: Frisco3 - A three-fluid model with continuous freeze-out for intermediate energy heavy-ion collisions

Abstract: Frisco3 is a novel 3-fluid hydrodynamical simulation model of relativistic heavy-ion reactions with a continuous transition from the fluid phase to the regime of free streaming hadrons. The time evolution of the reaction is consistently described in terms of three coupled ideal fluids, resembling the two nuclei and the fireball respectively, and a drain term, which is determined by the local thermal emissivity and the survival probability of produced hadrons given by their momentum differential, temperature and density dependent scattering rate in the medium. The drain from the fluid phase is irrecoverably transferred into the observable hadronic final state. Here, first benchmarking results on hadron multiplicities, rapidity and transverse momentum spectra and freeze-out properties related to the phase diagram are presented for Au+Au collisions ranging from 3 GeV to 20 GeV center of mass energy.

October  29 (online)

Mikhail Stephanov (University of Illinois, Chicago)

Slides  YouTube 

Host: Nu Xu

Title: QCD equation of state, critical point, and dynamics of fluctuations

Abstract: Recent theory advancements in the area of mapping the QCD phase diagram and locating the critical point in heavy-ion collisions will be discussed. Topics include the universal characteristics of fireball trajectories near the critical point, the hydrodynamic framework for non-Gaussian fluctuations, and the fluctuation freeze-out in accordance with conservation laws and the principle of maximum entropy.

October 22 (in person)

Raymond Ehlers (LBNL)

Slides  YouTube 

Host:  Peter Jacobs

Title: Multi-Observable Analysis of Jet Quenching Using Bayesian Inference

Abstract:  Bayesian inference is a flexible and incisive tool for determining underlying physical parameters, as well as characterizing consistency between data and models. It has been successfully applied to investigations of the quark-gluon plasma (QGP), utilizing a variety of measurements from RHIC and LHC. I will discuss a new multi-observable study of jet transport in the QGP using Bayesian Inference [1], for the first time incorporating all available inclusive hadron and jet suppression data. This study extends the previous JETSCAPE Bayesian Inference jet quenching analysis, which was based solely on selected inclusive hadron data. The multi-observable nature of the analysis enables exploration of correlations and differences between different probes and different kinematic ranges. Notably, tension is observed between calibrations based on hadron RAA for pT<30 GeV/c, and higher pT hadron and jet RAA data. We test the consistency of the theoretical formulation over a wide range of jet quenching data, and identifying those aspects of the formulation that are in tension with data. I will further discuss a first look at the inclusion of jet substructure measurements, as well as new methods and measurements for future Bayesian inference studies towards a comprehensive understanding of jet interactions in the QGP.

[1]: JETSCAPE Collaboration, arXiv: 2408.08247

October 15 (in person)

Sooraj Radhakrishnan (Kent State University/LBNL)

Slides  YouTube 

Host: Zhenyu Ye

Title: Measurement of jet $v_1$ to study path length dependent jet energy loss in heavy-ion collisions at $sqrt{s_{NN}}$ = 200 GeV at RHIC

Abstract: Studying the path length dependence of parton energy loss in the Quark Gluon Plasma (QGP) is cruical towards understanding the parton energy loss mechanism in the QGP. A path length asymmetry along impact parameter direction ($x$) exists for hard probes in heavy-ion collisions at finite rapidity, as the QGP bulk is tilted in reaction plane, while the hard scattering profile is not~\cite{ref1}. Jet $v_1$ ($\langle p_x/p_T \rangle$) measurements provide access to path length dependent energy loss of partons in the QGP. Such a measurement has several advantages. Energy loss can be accessed without measurements in p+p collisions. Event-by-event fluctuations in geometry do not contribute to $v_1$, unlike to the elliptic anisotropy, $v_2$. Another advantage is that the bulk $v_1$ is two orders of magnitude smaller than the bulk $v_2$, making the evolution of the first order anisotropy much weaker during the system evolution. 

In this talk we present the first measurement of charged jet and high $p_T$ charged hadron $v_1$ and $\langle p_x \rangle$ in heavy-ion collisions using Au+Au and Ru+Ru, Zr+Zr collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV by STAR. Centrality, jet $p_{\mathrm{T}}$ and radius dependence of the observables will be shown. We will also present an evaluation of the initial path length asymmetry utilizing models describing the measured pseudorapidity dependence of particle production in asymmetric collisions. We will also discuss future opportunities with event shape engineering for the first order anisotropy to further study the path length dependence of energy loss in the QGP. 

[1] PRL 123, 162301 (2019); PRL 120, 192301 (2018); PRC 72, 034907 (2005).

October 8 (online)

Chun Yuen Tsang (Kent State University)

Slides  YouTube 

Host: Zhenyu Ye

Title: Tracking the baryon number with nuclear collisions

Abstract: Baryon quantum number is believed to be conserved since baryogenesis in the early Universe. While fractionally charged valence quarks are understood conventionally to each carry a baryon number of 1/3, the baryon junction, a non-perturbative Y-shaped topology of neutral gluons, has also been proposed as an alternative entity tracing the baryon number. Neither scenario has been verified experimentally. The STAR Collaboration reports measurements at mid-rapidity of baryon number ($\boldsymbol{B}$) over the electric charge number difference ($\boldsymbol{\Delta Q}$) in isobar nuclear collisions, and the net-proton yield along rapidity in photonuclear collisions. A larger $\boldsymbol{B/\Delta Q}$ ratio and less asymmetric net-proton yield are observed than predicted from models assigning baryon number to valence quarks. Furthermore, the dependence of mid-rapidity net-hyperon yields, after corrected for s-quarks production suppression, on beam rapidity is also observed to be flavor blind, which is a signature of baryon junction. These findings, corroborated by previous measurements in Au+Au collisions, disfavor the valence quark picture.

September 24th (online)

Sanjin Benić (University of Zagreb)

Slides  YouTube 

Host: Wenbin Zhao

Title : Exclusive production and polarization of chi_c's as Odderon signatures in the DIS

Abstract: Exclusive chi_c production is sensitive to the C-odd colorless tri-gluon correlation in the t-channel - the long sought Odderon. While the Odderon escaped direct detections at HERA, the high luminosity of the future EIC machine can counteract the feeble Odderon amplitude. In our model computation [1] that also takes care of the constructive interference with the Primakoff background, the cross section for exclusive chi_c0, chi_c1 and chi_c2 production reaches about 10-100 fb. Thanks to the characteristically slow falling t-distribution, we estimate about a dozen events per month could be seen at the EIC.  In the forward region a contribution from the spin dependent Odderon is revealed and closely related to the gluon Sivers function [2]. Focusing on the axial vector chi_c1, the Coulomb tail (~1/|t|) of the Primakoff process is screened according to the Landau-Yang selection rule. Thus, the spin dependent Odderon can be directly probed in unpolarized gamma+p collisions including the UPCs. The two contributions (spin dependent Odderon and photon) can be disentangled by accessing the chi_c1 polarization via the angular distribution of its decay products revealing another potential signature for the Odderon at the EIC.

[1] S. Benic, A. Dumitru, A. Kaushik, L. Motyka, T. Stebel, Phys.Rev.D 110 (2024) 1, 014025

[2] S. Benic, A. Dumitru, A. Kaushik, L. Motyka, T. Stebel, 2407.04968 

September 17th (online)

Rui Zhang (Argonne National Laboratory)

Slides  YouTube 

Host: Yuxun Guo/ Bigeng Wang

Title : Resummation of Large Logarithm  in the Lattice Calculation of Generalized Parton Distributions and Meson Distribution Amplitudes

Abstract:  The generalize parton distributions  (GPDs) are essential for us to understand the 3D imaging of the proton in the longitudinal momentum fraction $x$ and transverse impact parameter space. Meson distribution amplitudes (DAs) describe the wave function of meson as a quark-antiquark pair in the infinite-momentum frame. They are important inputs for hard exclusive processes, but their $x$-dependence  are difficult to extract from experimental data. The large momentum effective theory (LaMET) provides an approach to directly calculate the $x$-dependence of these partonic observables on a Euclidean lattice with a perturbative matching. When any of the parton’s momentum becomes soft, the corresponding logarithm in the matching kernel becomes large at higher orders of perturbation theory, which requires a resummation. But the resummation for these off-forward matrix elements are difficult due to their multi-scale nature.

In this talk, we propose an approach to resum the large logarithms in the LaMET matching of GPDs and DAs, and apply it to a GPD model and the lattice calculation of DA. After resummation, we can estimate the perturbative uncertainties, and demonstrate which region of $x$ can be reliably calculated from lattice through the large momentum effective theory. 

September 10ed (online)

 Shu-Yi Wei (ShanDong University)

 Slides   Youtube 

Host: Wenbin Zhao

Title : Spin effects in unpolarized collisions

Abstract: 

The hadronization of energetic partons is described by fragmentation functions. The spin-dependence was mainly investigated in polarized colliders or weak-interaction-dominating processes. Therefore, the quantitative study of spin-dependent fragmentation functions is still in its infancy. However, quiet a few spin effects emerge in unpolarized high-energy collisions. Therefore, unpolarized colliders are also capable of investigating spin-dependent fragmentation functions. In this talk, I will mainly present two topics: (1) the helicity correlation of back-to-back dihadron in unpolarized ee, ep, and pp collisions (arXiv:2301.04096, 2309.09487, 2404.19202); (2) the azimuthal-angle-dependent polarizations in unpolarized semi-inclusive deeply inelastic collisions (arXiv:2108.07740).

September 3ed (In person)

Andrea Shindler (LBNL & RWTH Aachen University)

Youtube

Host: Andre Walker-Loud

Title : A new method to determining parton distribution functions from lattice QCD

Abstract: 

We present a novel approach to determine moments of parton distribution functions (PDFs) of any order using lattice QCD computations. This method leverages the gradient flow for fermion and gauge fields, enabling more precise calculations and resolving a long-standing problem of direct calculation of moments of PDF from lattice QCD. By utilizing flowed matrix elements of twist-2 operators, which renormalize multiplicatively, we achieve the matching with physical matrix elements through the application of continuum symmetries.

Our work includes the computation of matching coefficients at one-loop in perturbation theory for moments of any order in the flavor non-singlet case. We also provide explicit examples of operators suitable for lattice QCD computations. The multiplicative renormalization and matching process is independent of the choice of Lorentz indices, allowing the use of temporal indices for twist-2 operators of any dimension. This flexibility is expected to significantly enhance the signal-to-noise ratio in the computation of moments.

We present preliminary numerical results for moments of the pion PDFs up to $\left\langle x^6 \right\rangle$, demonstrating the successful resolution of the renormalization challenge. This method shows great potential for a first-principle, non-perturbative determination of parton distribution functions, offering a new robust approach to overcoming existing theoretical and numerical challenges.

Tuesday, July 16th, 3:30PM (in-person and on zoom)

Jian Liang (South China Normal University) 

Slides   Youtube

Host: Keh-Fei Liu

"Theta Induced Nucleon EDM, CP-Violating Pion-Nucleon Coupling & Pion Mass Shift from Lattice QCD"

We report our lattice QCD calculation of the nucleon electric dipole moment (EDM), the CP-violating pion-nucleon coupling and the pion mass shift induced by the theta term. We use lattice chiral fermions in our calculation, which provides a fermionic definition of the topological charge exhibiting small discrete effects. Also, the use of chiral fermions guarantees a correct chiral limit even at finite lattice spacings and enables us to reliably extrapolate our result from heavy pion masses to the physical point. With the help of the cluster decomposition error reduction (CDER) technique, we have obtained so far the best results for the nucleon EDM. The CP-violating pion-nucleon coupling and the pion mass shift are directly calculated on the lattice for the first time.

Tuesday, May 28th, 3:30PM (in-person and on zoom)

Meijian Li (Santiago de Compostela Univeersity)

Host: Xin-Nian Wang

Slides   Youtube

"Scattering and gluon emission of a dressed quark in colored field"

Following the non-perturbative light-front Hamiltonian formalism developed in the preceding works [Phys. Rev. D 104, 056014 (2021), Phys. Rev. D 108, 036016 (2023)], we investigate the scattering and gluon emission of dressed quark states inside a SU(3) colored background field. We consider the scenario in deep inelastic scattering and in heavy ion collisions, where the quark originates from far outside the background field and is described by the light-front wavefunction of the QCD eigenstate in the |q>+|qg> Fock space. We perform numerical simulations of the real-time quantum state evolution of an initially dressed quark state at various energy and medium configurations. With the obtained light-front wavefunction of the evolved state, we extract the quark jet transverse momentum distribution, the cross section, and the gluon emission rate. This investigation provides a novel systematic description of the quark scattering process inside colored medium using a non-perturbative formalism.

Friday, May 10th, 10am (on zoom)

Jaime Norman  (University of Liverpool)

Slides   Youtube

Host: Peter Jacobs

Probing jet energy redistribution and broadening in heavy-ion collisions with ALICE at the LHC

Heavy-ion collisions at the LHC generate the hottest form of matter that can be created in a lab - 100 thousand times hotter than the centre of the sun - where hadronic matter exists in a deconfined state of quarks and gluons, the ‘Quark-Gluon Plasma’ (QGP). Jets - collimated sprays of hadrons originating from a high-momentum quark or gluon - are generated in heavy-ion collisions, and their interactions with the QGP provide unique probes of its properties. A key question in the study of the QGP is whether its short-distance structure can be resolved and studied, and a ‘scattering experiment’ involving jets, analogous to Rutherford’s experiment which determined the structure of the atom, offers one of the most promising ways to achieve this. Such effects are expected to be most prominent at low jet transverse momentum ($p_\mathrm{T}$), which is where jet measurements are also sensitive to wake effects due to response of the QGP itself to the jet-medium energy transfer. Measurements that are differential in jet $p_\mathrm{T}$, jet radius $R$, and acoplanarity (deflection angle) may be able to disentangle these various mechanisms.  

This talk presents a new measurement of charged-particle jets recoiling from a trigger hadron in proton-proton and central lead-lead collisions by ALICE - the LHC experiment dedicated to studying heavy-ion collisions. The measurement is performed using a background-subtraction technique which provides a precise data-driven subtraction of the large uncorrelated background contaminating the measurement, uniquely enabling the measurement of jet production and acoplanarity over a wide phase space, including the low jet $p_\mathrm{T}$ region for large $R$. 

Tuesday, April 30th, 3:30PM (in-person and on zoom)

Dr. Daniel Hackett (Fermilab)

Youtube Slides

Host: Dimitra Pefkou

"Machine-learned flows for QCD"

Numerical lattice quantum field theory is one of our important tools for investigating quantum chromodynamics (QCD), but what physics may be treated is limited by presently available computing resources. Recent work suggests that machine learning techniques may provide algorithmic advances that could open access to calculations which are presently intractable. In particular, normalizing flows are machine-learned maps between different lattice theories which can be used as components in exact sampling and inference schemes. Ongoing work yields increasingly expressive flows on gauge fields, but it remains an open question how flows can best be used to improve lattice QCD at state-of-the-art scales. This talk will review this effort and discuss recent progress, in particular several applications which are viable with presently available flows.

Tuesday, April 23rd, 3:30PM (in-person and on zoom)

Dr. Joseph Karpie (Jefferson Lab)

slides Youtube

Host: Dimitra Pefkou

"Calculating what you're made of: Partons and the Lattice"

Many interactions with nuclei can be described in terms of convolutions of universal parton distributions. These parton distributions describe the way quarks and gluons distribute themselves within the hadrons in terms of their fraction of the total momentum. Over the past decade these distributions have been inferred from matrix elements calculated with Lattice QCD in analogous methods to those used for experiment. From these data the evolution of the parton distributions can also be determined independent of a PDF analysis. Also, the Lattice QCD matrix elements can be included as prior information in global analysis of experimental cross sections leading to significantly improved understanding of the structure in a wide range of the momentum fraction.

Tuesday, April 9th, 3:30PM (in-person and on zoom)

Dr. Ting-Wai Chiu (National Taiwan University)

slides Youtube

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, March 26th, 3:30PM (in-person and on zoom)

Dr. Mesut Arslandok  (Yale University)

slides Youtube

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 12th, 3:30PM (in-person and on zoom)

Dr. Ashish Pandav (Lawrence Berkeley National Lab)

slides Youtube

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)

slides Youtube

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)

slides Youtube

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 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)

slides Youtube

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 9th, 3:30PM (in-person and on zoom)

Dr. Rajan Gupta (Los Alamos National Lab)

slides Youtube

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.

Tuesday, December 12th, 2023, 3:30 PM PST (in-person & zoom) 

Dr. Peter Jacobs (LBL)

Slides Youtube

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.

Thursday,  December 7th, 2023  3:30 PM PST (in-person & zoom)

Dr. Gang Wang (UCLA)  

Slides Youtube

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.

 Monday, November 13th, 2023, 3:30 PM PST (in-person & zoom) 

Dr. Paul Caucal (Nantes)

Slides Youtube

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

 Tuesday, October 31st, 2023, 3:30 PM PST (in-person & zoom) 

Dr. Shohini Bhattacharya (BNL)

Slides 

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 17th, 2023, 3:30 PM PST (zoom) 

Dr. Toshiyuki Gogami (Kyoto University)

Slides Youtube

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.

Thursday, September 21st, 2023, 3:30 PM PST (zoom) 

Dr. Renaud Boussarie (CPHT, Ecole Polytechnique)

Slides

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, 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)

Slides Youtube

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 16th, 2023 3:30 PM PST (zoom & in person)

Dr. Wenqing Fan (LBNL)

Slides Youtube

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,  April 25th, 2023  3:30 PM PST (zoom)

Dr. Norbert Herrmann (Heidelberg University)  

Host: Nu Xu

Youtube

"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 4th, 2023  3:30 PM PST (zoom)

Dr. John Terry (LANL)  

Host: Farid Salazar

Slides Youtube

"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.

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

Slides Youtube

"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.

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"

Slides Youtube 

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"

Youtube

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"

Slides     Youtube

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"

Slides      Youtube

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"

Slides    Youtube

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.

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/. 

Thursday, October 20th,   2022  3:30 PM PDT 

In-person (Theory Lounge 70-228) & Zoom

Mr. Henry Klest  (Stony Brook University)
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

Slides Youtube

   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, 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

Slides Youtube

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

Slides Youtube

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

Slides Youtube

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.