Hadron Ion Tea (HIT) Seminar

[formerly Heavy Ion Tea Seminar]

Nuclear Science Division

Lawrence Berkeley National Laboratory

HIT seminars are typically on Tuesdays at 3:30pm Pacific Time

Current Organizers: Nicole Apadula, Sooraj Radhakrishnan, André Walker-Loud, Xin-Nian Wang

HIT zoom link

Tues. 2021.05.11, 12:00 PM, Virtual Zoom HIT

Prof. Jesus Guillermo Contreras Nuno (Czech Technical University)

Diffractive vector meson photoproduction: a Swiss army knife for QCD

Abstract: Diffractive vector meson production is a deceptively simple process which allows us to ask several different questions about QCD in a relatively clean enviroment. In this talk I will present an overview of recent experimental results and discuss some of their implications,mainly regarding the search for stauration effects.

Upcoming seminars

4 May, 2021 - Joseph Kapusta (Univ of Minnesota)

11 May, 2021 - Jesus Guillermo Contreras Nuno (Czech Technical University)

18 May, 2021 - Vincenzo Greco (Istituto Nazionale di Fisica Nucleare) (start at 1:30 pm)

25 May, 2021 - Dennis Perepelitsa ( Univ of Colorado Boulder)

1 June, 2021 - Nu Xu (LBNL)

8 June, 2021 - James Brandenburg (Stony Brook Univ)

15 June, 2021 - James Mulligan (LBNL)

Tues. 2021.06.15, 3:30 PM, Virtual Zoom HIT

Dr. James Mulligan (LBNL)


Jet substructure: from proton-proton to heavy-ion collisions

Jet substructure, defined by observables constructed from the distribution of constituents within a jet, provides the versatility to tailor observables to specific regions of QCD radiation phase space. This flexibility allows us to test not only our understanding of perturbative QCD but also the nature of nonperturbative effects including hadronization — and has resulted in jet substructure becoming an essential tool to study rare event topologies in searches for new physics. In this talk, I will highlight recent jet substructure measurements at the LHC and RHIC. I will discuss measurements in proton-proton collisions, which enable differential tests of our understanding of perturbative QCD, and measurements in heavy-ion collisions, which provide exciting new opportunities to reveal the nature of the quark-gluon plasma.

Tues. 2021.05.04, 3:30 PM, Virtual Zoom HIT

Prof. Joseph Kapusta (Univ of Minnesota)



Neutron Stars with a Crossover Equation of State

Abstract: The question of whether quark matter exists in neutron stars is a long standing one. Generally one finds that a first order phase transition from baryons to quarks softens the equation of state so much that the star would collapse into a black hole. We consider a crossover equation of state, similar to the crossover that is found in lattice QCD studies at finite temperature and zero or small baryon chemical potentials. We find that with reasonable parameters it may be possible to support neutron stars up to about 2.2 solar masses. In that case 1 to 10% of the pressure would be contributed by quark matter in the central core of the highest mass stars.

Joint Nuclear Science and Physics Division Seminar on muon g-2

Tuesday, April 27, 10:30am - 12:45pm


Zoom Meeting Link

Meeting ID: 927 0993 8569

Passcode: 843893

Add to your calendar

We are having a special seminar followed by a panel discussion on the recent g-2 result for the muon, with an emphasis on the theoretical prediction for this quantity.

10:30am : Welcome

10:35am: Laurent Lellouch

11:10am: Martin Hoferichter

11:40am: Panel discussion + audience question/answer

Panelists: Gilberto Colangelo (chair), Aida El-Khadra, Christoph Lehner, Bill Marciano and Thomas Teubner

Laurent Lellouch
Gilberto Colangelo
Bill Marciano
Martin Hoferichter
Aida El-Khadra
Thomas Teubner

Christoph Lehner

Tues. 2021.04.20, 3:30 PM, Virtual Zoom HIT

Dr. Ivan Vitev (LANL)



Jet production in e+A collisions at the EIC

Jet production and jet substructure in reactions with nuclei at future electron ion colliders will play a preeminent role in the exploration of nuclear structure and the evolution of parton showers in strongly-interacting matter. In the framework of soft-collinear effective theory, generalized to include in-medium interactions, we present the first theoretical study of inclusive jet cross sections and the jet charge at the EIC. Predictions for the modification of these observables in electron-gold relative to electron-proton collisions reveal how the flexible center-of-mass energies and kinematic coverage at this new facility can be used to enhance the signal and maximize the impact of the electron-nucleus program. Importantly, we demonstrate theoretically how to disentangle the effects from nuclear parton distribution functions and the ones that arise from strong final-state interactions between the jet and the nuclear medium. A comparison to the modification of inclusive hadron production is also shown.

Tues. 2021.04.13, 4:30 PM, Virtual Zoom HIT

Prof. Xiaofeng Luo (Central China Normal Univ)


QCD Critical Point and Net-Proton Number Fluctuations

Understanding the properties of quark matter and its phase structure can enhance our knowledge of universe evolution and the structure of visible matters. In the last two decades, many experimental evidences for the strongly interacting quark-gluon plasma (sQGP) have been observed in high energy heavy-ion collisions. Therefore, exploring the QCD phase structure at high baryon density, such as mapping the 1st order phase boundary and finding the QCD critical point, becomes one of the most important goals of the heavy-ion collisions. During 2010-2017, RHIC has finished the first phase of Beam Energy Scan program (BES-I), and STAR experiment has collected the data of Au+Au collisions at various collision energies from 200 to 7.7 GeV. To confirm the intriguing observations at BES-I, RHIC has started the second phase of beam energy scan program (BES-II) since 2018, focusing on the energies below 27 GeV. From 2018 to 2020, STAR experiment has taken the data of high statistics Au+Au collision at 9.2, 11.5, 14.6, 19.6 and 27 GeV (collider mode) and 3.0 - 7.7 GeV (fixed target mode). In this talk, I will discuss the recent experimental progress for exploring the QCD phase structure at RHIC-STAR experiment, especially focusing on the QCD critical point search. New facilities aiming for high baryon density region and future plan will be also discussed.



Tues. 2021.04.06, 3:30 PM, Virtual Zoom HIT

Prof. Jingfeng Liao (Indiana Univ)




Toward seeing the chiral magnetic effect at long last

Quantum anomaly is a fundamental feature of chiral fermions. In chiral materials, the microscopic anomaly leads to nontrivial macroscopic transport processes such as the chiral magnetic effect (CME), which has been in the spotlight lately across disciplines of physics. The quark-gluon plasma (QGP) created in relativistic nuclear collisions provides the unique example of a chiral material consisting of intrinsically relativistic chiral fermions. The potential discovery of CME in QGP is of utmost significance, with extensive experimental searches carried out over the past decade. The path toward discovering it in heavy-ion collision experiments, however, has been rocky, due to relatively weak signal and strong background contamination. About 12 years after the first hint of possible CME signal reported at QM2009, excitement is mounting amid the expected release of analysis results later this year from a decisive isobar collision experiment. In this talk, I will discuss the early developments of this “hunt”, the painstaking process of recognizing and facing the background challenges and the key progress in remediating them. I will also discuss the status and prospect of relevant theoretical developments, highlighting the quantitative predictions for signatures of CME in the collisions of isobars.

Tues. 2021.03.30, 3:30 PM, Virtual Zoom HIT

Prof. Dima Kharzeev (Stony Brook Univ)


Mass radius of the proton


The mass radius is a fundamental property of the proton that so far has not been determined from experiment. Basing on my recent paper arXiv:2102:00110, I will show that the mass radius of the proton can be rigorously defined through the formfactor of the trace of the energy-momentum tensor (EMT) of QCD in the weak gravitational field approximation, as appropriate for this problem. I will then demonstrate that the scale anomaly of QCD enables the extraction of the formfactor of the trace of the EMT from the data on threshold photoproduction of J/ψ and Υ quarkonia, and use the recent GlueX Collaboration data to extract the r.m.s. mass radius of the proton R_m = 0.55 ± 0.03 fm. The extracted mass radius is significantly smaller than the r.m.s. charge radius of the proton R_C = 0.8409 ± 0.0004 fm. I will discuss the possible origin of this difference, and outline future measurements needed to determine the mass radius more precisely.

Tues. 2021.03.23, 3:30 PM, Virtual Zoom HIT

Dr. Kei Nagai (LANL)

Asymmetry of antimatter in the proton from SeaQuest and SpinQuest perspectives


Naively, the amounts of dbar and ubar in the proton were expected to be the same based

on the flavor-independence of the strong coupling. However, the muon deep inelastic

scattering experiment NMC at CERN found dbar>ubar in the proton. Drell--Yan experiments also obtained the results consistent with it. The Drell--Yan experiment

E866 at Fermilab showed that dbar(x)/ubar(x)>1.0 for 0.015 < x < 0.20. It also showed dbar(x)/ubar(x)<1.0 at large x (x~0.3), although it is consistent with 1.0 within statistical uncertainty. SeaQuest is a Drell--Yan experiment at Fermilab that measured the antiquark flavor asymmetry dbar/ubar precisely for a wide x range (0.13 < x < 0.45) including the intriguing region from E866. It uses a 120 GeV proton beam extracted from Fermilab Main Injector colliding with liquid hydrogen and deuterium targets. The antiquark flavor asymmetry dbar(x)/ubar(x) is derived from the cross section ratio of proton-deuterium to proton-proton Drell--Yan processes. SeaQuest results were published on Nature in February 2021. In this talk, the contents of Nature paper will be mainly presented. In addition to that, the perspective of the SpinQuest experiment will be also discussed.

Tues. 2021.03.16, 3:30 PM, Virtual Zoom HIT

Dr. Xuan Li (Los Alamos National Laboratory)


Explore hadronization through heavy flavor probes at the Electron-Ion Collider


How fundamental elementary blocks: quarks and gluons form into visible matter remains as a long-standing unresolved question. Such process known as the hadronization, can not be directly calculated by perturbative Quantum Chromodynamics (QCD). Existing e+e−, e + p, p + p, p + A and A + A experimental results provide limited constraints on the hadronization process either due to the limited kinematic reach or the complexity of hadron and heavy ion collision systems. The proposed high luminosity high energy Electron-Ion Collider (EIC) will provide a clean environment to explore the hadronization processes in vacuum and a heavy nucleus within a wide kinematic phase space. Heavy flavor products such as a D-meon or a charm jet at the EIC provide enhanced sensitivities to the nuclear transport properties in medium. Moreover, they will provide strong discriminating power to separate the hadronization happened inside or outside the nuclear medium. In this talk, I will discuss about studies of heavy flavor hadron and jet reconstruction in simulation and the corresponding physics studies associated with the hadronization process, such as the flavor dependent hadron nuclear modification factor in electron+nucleus collisions. Initial design and performance of a proposed forward (proton/nuclei going direction) silicon tracking detector, which is essential to carry out these measurements at the EIC will be shown as well.

Tues. 2021.03.09, 1:30 PM, Virtual Zoom HIT

Dr. Urs Wiedemann (CERN)


Flow and jet quenching in small systems


As a function of system size and center-of-mass energy, signatures of collectivity are known to arise smoothly and without any sharp threshold in ultra-relativistic proton-proton (pp), proton-nucleus and nucleus-nucleus collisions (AA). Yet, the physics concepts invoked in phenomenological descriptions of the smallest (pp) and the largest (central AA) hadronic collision systems are maximally different. Our baseline picture of pp collisions is a free-streaming but fragmenting partonic system in which final state interactions may be treat as perturbations. Our baseline picture of central heavy ion collisions is a perfect fluid, deviations of which are parametrized in terms of dissipative fluid dynamic properties. Given that the size of the smallest and the largest collision systems differ by only one order of magnitude, and given that the entire size-dependence is experimentally accessible, there are strong motivations for developing a phenomenological description that smoothly interpolates between almost free-streaming and almost perfect fluidity as a function of system size. In this talk, I discuss some of the resulting theoretical challenges and open experimental issues. I emphasize that such a phenomenological program can give access to some fundamental properties of hot QCD matter that escape a purely fluid-dynamic analysis of heavy ion data.

Tues. 2021.03.02, 3:30 PM, Virtual Zoom HIT

Prof. Chun Shen (Wayne State Univ)



Dynamical modeling of the initial energy-momentum and baryon charge distributions for heavy-ion collisions at RHIC and LHC

Heavy-ion collisions at different beam energies offer us a unique opportunity to study the QGP properties in the $T$-$\mu_B$ QCD phase diagram. Building upon Ref. [1], we present an improved three-dimensional dynamical initialization model for heavy-ion collisions by implementing local energy-momentum conservation and baryon charge fluctuations at string junctions [2]. These improvements lead to an excellent description of the charged hadron and net proton rapidity distributions in Au+Au collisions from 7.7 to 200 GeV. By keeping all model parameters fixed, we extrapolate our model to asymmetric (p, d, 3He)+Au collisions at RHIC BES energies as well as p+Pb, O+O, and Pb+Pb at LHC energies. We achieve a good description of the measured particle rapidity distributions for those collision systems, demonstrating our model’s predictive power.

[1] C. Shen and B. Schenke, “Dynamical initial state model for relativistic heavy-ion collisions,” Phys.Rev. C97 (2018) no.2, 024907

[2] D. Kharzeev, “Can gluons trace baryon number?,” Phys. Lett. B 378, 238 (1996)

Tues. 2021.02.23, 3:30 PM, Virtual Zoom HIT

Prof. Hengtong Ding (Central China Normal Univ)


Correlated Dirac eigenvalues and axial anomaly in chiral symmetric QCD


The phenomenon of anomaly plays an important role in quantum field theory. In QCD how axial anomaly manifests itself in the two-point correlation functions of iso-triplet scalar and pseudo-scalar mesons affects the nature of chiral phase transition. In this talk I first review current studies of the fate of UA (1) anomaly in the finite temperature lattice QCD, and then propose novel relations between the quark mass derivatives of Dirac eigenvalue spectrum and correlation functions among eigenvalues in order to study the microscopic origin of the axial anomaly. We finally show our results in the chiral and continuum limit in (2+1)-flavor lattice QCD at 1.6Tc. Our results suggest that the axial anomaly is driven by the weakly interacting (quasi-)instanton gas motived eigenvalue spectrum above 1.6Tc and the chiral phase transition is of 2nd order and belongs to 3-d O(4) universality class (talk is based on https://arxiv.org/abs/2010.14836).

Tues. 2021.02.16, 3:30 PM, Virtual Zoom HIT

Prof. Michael Strickland (Kent State Univ)


Non-equilibrium attractor in high-temperature QCD plasmas


I will discuss a recent paper in which my collaborators and I established the existence of a far-from-equilibrium attractor in weakly-coupled gauge theory that goes beyond the usual hydrodynamic attractor picture. We demonstrated that the resulting far-from-equilibrium evolution is insensitive to certain features of the initial condition, including both the initial momentum-space anisotropy and initial occupancy. We found that this insensitivity extends beyond the energy-momentum tensor to the detailed form of the one-particle distribution function. Based on our results, I will assess different procedures for reconstructing the full one-particle distribution function from the energy-momentum tensor along the attractor and discuss implications for the freeze-out procedure used in the phenomenological analysis of ultra-relativistic nuclear collisions.


  1. Dekrayat Almaalol, Aleksi Kurkela, and Michael Strickland, Phys. Rev. Lett. 125, 122302 (2020)

  2. M. Strickland, Journal High Energy Physics 2018, 128 (2018).

Tues. 2021.02.9, 3:30 PM, Virtual Zoom HIT

Prof. Takafumi Niida (University of Tsukuba)


Global polarization of \Xi and \Omega hyperons in heavy-ion collisions


Global polarization in heavy-ion collisions arises from the partial conversion of the orbital angular momentum of colliding nuclei into the spin angular momentum of particles produced in the collisions. The STAR Collaboration observed \Lambda global polarization in Au+Au collisions at \sqrt{s_{NN}} = 7.7—200 GeV, indicating a thermal vorticity of the system. Based on thermal models, particles with the same spin are expected to have the same polarization, while other effects might contribute to the polarization and change the picture. In this talk, the first measurements of the global polarization of spin s=1/2 \Xi and spin s=3/2 \Omega hyperons in heavy-ion collisions will be presented and the physics implications will be discussed.

Tues. 2021.02.2, 3:30 PM, Virtual Zoom HIT

Prof. Huey-Wen Lin (Michigan State University)



Mapping Nucleon Parton Distributions with Lattice QCD

The strong force which binds hadrons is described by the theory of quantum chromodynamics (QCD). Determining the character and manifestations of QCD is one of the most important and challenging outstanding issues necessary for a comprehensive understanding of the structure of hadrons. Within the context of the QCD parton picture, the parton distribution functions (PDFs) have been remarkably successful in describing a wide variety of processes. However, these PDFs have generally been confined to the description of collinear partons within the hadron. New experiments and facilities provide the opportunity to additionally explore the three-dimensional structure of hadrons, which can be described by generalized parton distributions (GPDs) for example.

In recent years, a breakthrough was made in calculating the Bjorken-x dependence of PDFs in lattice QCD by using large-momentum effective theory (LaMET) and other similar frameworks. The breakthrough has led to the emergence and rapid development of direct calculations of Bjorken-x dependent structure.

Tues. 2021.01.26, 1:30 PM, Virtual Zoom HIT

Dr. Yi Chen, MIT



Constraining the jet transport coefficient q-hat in heavy-ion collisions with Bayesian analysis

The jet transport coefficient qhat is a characterization of the properties of the interaction between high energy parton and the quark-gluon plasma, created during relativistic heavy-ion collisions. I will present a new analysis by the JETSCAPE Collaboration of the dependence of qhat on jet energy, jet virtuality, and medium temperature. The analysis utilizes Bayesian parameter estimation techniques to compare theoretical calculation and experimental data of inclusive hadron suppression spanning a wide range of transverse momentum, at both RHIC and LHC center-of-mass energies. The correlation of the experimental uncertainties is an important piece of the analysis and is accounted for. Simulation is performed using the JETSCAPE framework, with a multi-stage approach based on the MATTER and LBT jet quenching models We will also discuss prospects of additional analyses to better constrain additional properties of the quark-gluon plasma.

Tues. 2021.01.26, 1:30 PM, Virtual Zoom HIT

Dr. Yi Chen, MIT



Search for the elusive jet-induced diffusion wake in Z-jets with 2D jet tomography

Diffusion wake is an unambiguous part of the jet-induced medium response in high-energy heavy-ion collisions that leads to a depletion of soft hadrons in the opposite direction of the jet propagation. New experimental data on $Z$-hadron correlation in Pb+Pb collisions at the Large Hadron Collider show, however, an enhancement of soft hadrons in the direction of both the $Z$ and the jet. Using a coupled linear Boltzmann transport and hydro model, we demonstrate that medium modification of partons from the initial multiple parton interaction (MPI) gives rise to a soft hadron enhancement that is uniform in azimuthal angle while jet-induced medium response and soft gluon radiation dominate the enhancement in the jet direction. After subtraction of the contributions from MPI with a mixed-event procedure, the diffusion wake becomes visible in the near-side $Z$-hadron correlation. We further employ the longitudinal and transverse gradient jet tomography for the first time to localize the initial jet production positions in $Z/\gamma$-jet events in which the effect of the diffusion wake is apparent in $Z/\gamma$-hadron correlation even without the subtraction of MPI.

Tues. 2021.01.12, 3:30 PM, Virtual Zoom HIT

Prof. Jaki Noronha-Hostler, University of Illinois at Urbana-Champaign



What can we learn from heavy neutron stars?

The observation of gravitational waves from a blackhole-mystery object binary opens the possibility for heavy neutron stars of 2.5 solar masses (potentially seen in GW190814). If this mystery object is a neutron star of 2.5 solar masses, it poses direct challenges to models of the equation of state. Interestingly, introducing non-trivial structure in the speed of sound sourced by changes in the degrees of freedom (possibly quarks) of ultra-dense matter can resolve this conflict, which may have large ramifications in nuclear and astrophysics. However, for a clear smoking gun signature of the mystery object being a neutron star, one requires a measurement of the tidal deformability that is non-zero. Because the predicted values are very small, a tenfold increase in sensitivity may be needed to test this possibility with gravitational waves, which is feasible with third generation detectors. Finally, I will comment on opportunities in heavy-ion collisions that exist for further constraining the equation of state relevant to neutron stars.