# Hadron Ion Tea (HIT) Seminar Series

[formerly the Heavy Ion Tea Seminars]

Nuclear Science Division

Lawrence Berkeley National Laboratory

# HIT seminars are on Tuesdays and Thursdays at 3:30pm Pacific Time (unless otherwise noted)

Organizers: Shujie Li, Dimitra Pefkou, Nu Xu, & Wenbin Zhao

Previous seminars can be viewed on our HIT Youtube Channel

# Upcoming seminars

Welcome to our Hadron-Ion Tea Seminar Series in 2024! All talks are available on zoom, some are in-person as well - we hope you join us!

Tuesday, March 5th, 3:30PM (in-person and on zoom)

Dr. Bigeng Wang (University of Kentucky)

Host: Dimitra Pefkou

"Trace anomaly form factor from lattice QCD"

The hadron mass can be obtained through the calculation of the trace of the energy-momentum tensor (EMT) which includes the trace anomaly and sigma terms. The anomaly due to conformal symmetry breaking is believed to be an important ingredient for hadron mass generation and confinement. For the nucleon, the trace anomaly term is the dominating contribution to its mass. For the pion, the trace anomaly term contributes about half of the mass and approaches zero toward the chiral limit, just like the sigma term due to chiral symmetry breaking. To understand what kind of structure change can facilitate this attribute, the calculation of the spatial distribution of the trace anomaly is necessary.

In this talk, I will present the calculation of the glue trace anomaly form factors of the pion and the nucleon from lattice QCD. By performing a two-dimensional Fourier transform on the form factors in the infinite momentum frame with no energy transfer, we obtain the corresponding spatial distributions.

For the pion, we calculate its mass radius from the glue trace anomaly to be 4.6(0.6)(1.3) fm with possibly large systematic errors. For the nucleon, we calculate its mass radius to be 0.89(10)(07) fm, which is consistent with several recent calculations from gravitational form factors (GFF). We find the pion's spatial distribution changes sign, as does its form factor, for light quark masses. This explains how the trace anomaly contribution to the pion mass approaches zero toward the chiral limit.

arXiv reference: https://arxiv.org/abs/2401.05496

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

Dr. Ashish Pandav (Lawrence Berkeley National Lab)

Host: Nu Xu

"High Moments of Net-proton Measurements in STAR at RHIC"

The Quantum-ChromoDynamics (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 19th, 3:30PM (in-person and on zoom)

Dr. Xiang Gao (Physics Division, Argonne National Laboratory)

Host: Wenbin Zhao

"Parton distributions from boosted fields in the Coulomb gauge"

Over the past few years, significant progress has been made in computing parton distributions from lattice QCD within the framework of large momentum effective theory (LaMET). The light-cone parton distributions were derived from gauge-invariant equal-time corrrelators with large momentum boost. In this talk, we introduce a new approach to calculate parton distributions from correlations of boosted quarks and gluons in the Coulomb gauge (CG), without Wilson lines. This new method can substantially improve statistical precision and simplify renormalization, thus providing a more efficient way to calculate parton distributions in lattice QCD, particularly for 3D distributions. We verified the validity of this method at next-to-leading order in perturbation theory and used it to calculate the pion valence quark PDF. Additionally, we derived the Collins-Soper kernel from a CG quasi-TMD up to $b_T$=4.2 GeV^{-1}, further demonstrating its effectiveness and potential for future lattice calculations.

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

Dr. Masuk Arslandok (Yale University)

Host: Volker Koch

"Exploring the QCD phase diagram and hunting for new physics via heavy-ion collisions in ALICE at the LHC"

Predictions based on the theory of strong interaction, QCD, imply that, at sufficiently high

energy densities, nuclear matter transforms into a state called quark-gluon plasma (QGP), in

which quarks and gluons move freely. Ultrarelativistic heavy-ion collisions are ideal

environments to study this phase transition, which can be explored via fluctuations of conserved

charges such as electric charge, strangeness and baryon number. Moreover, these collisions

offer opportunities to probe physics beyond the Standard Model, which will become feasible

during the data collection periods of LHC Runs 3 and 4 thanks to the upgraded gas electron

multiplier-based time projection chamber of the ALICE detector.

In this talk, I will give an overview of the insights gained from the results of the ALICE

collaboration regarding the QCD phase diagram, along with a novel program aimed at searching

for new physics beyond the Standard Model utilizing the ALICE TPC. Finally, I will wrap up by

discussing the future perspectives of the ALICE collaboration in both of these endeavors, looking

ahead to the future heavy-ion detector, called ALICE3, planned for the early 2030s.

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

Dr. Joseph Karpie (Jefferson Lab)

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, May 14th, 3:30PM (in-person and on zoom)

Dr. Anar Rustamov (GSI)

Host: Nu Xu

"Decoding the QCD Phase Transition via Cumulants of Particle Multiplicity Distributions in High-Energy Nuclear Collisions"

Abstract coming soon!

Tuesday, January 30th, 3:30PM (in person) Postponed, TBD

Dr.Dipangkar Dutta (Mississippi State University)

Host: Shujie Li

"Tagged DIS at JLab"

Abstract coming soon!