# 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, Jennifer Rittenhouse West and Xin-Nian Wang

Previous seminars can be viewed on our HIT Youtube Channel

Talks in 2021

### Wednesday, 06.29.2022, 3:30 PM PDT

Joint Nuclear Theory/HIT seminar! Special date on Wednesday!

Dr. Jennifer Rittenhouse West (LBNL)

Host: Xin-Nian Wang

Diquark Formation as a Breakthrough of Fundamental QCD into Nuclear Physics

A diquark bond formed from valence quarks across a nucleon-nucleon pair has been proposed as the fundamental quantum chromodynamics (QCD) physics causing short-range correlations (SRC) in nuclei. Short-range correlated nucleon-nucleon pairs and the nucleon shell model are the basis for nuclear physics, with SRC accounting for 20% of the nucleons in a nucleus. While SRC have been extensively studied both experimentally and theoretically, notably by the CLAS collaboration in recent years, their underlying cause at the QCD level has remained a mystery. The diquark formation model, if shown to be the cause of SRC in nuclei, represents a breakdown of the assumption of scale separation in effective field theories. Rather than a boundary between scales, however fuzzy and broad, a case is made in this work for diquark formation as a direct breakthrough of the underlying theory, capturing 20% of the physics of nuclear structure.

### Postponed to a future date, 12:00 PM PST

Dr. Norbert Herrmann (GSI)

Status and Physics of the CBM experiment at FAIR

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 2025-26. 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 which will provide new insights to topics like
equation-of-state of dense nuclear matter, the possible phase transition from hadronic to partonic phase, and chiral symmetry restoration. The experimental program that covers the measurement of (multi-) strange particle production, dilepton spectroscopy, collective flow and light hypernuclei will be discussed as well as the status of the detector subsystems and their performance in the currently operated demonstrator mCBM at SIS18

### TBD

Dr. Shuzhe Shi (NYU at Stonybrook)

Host:

Implications of the isobar run results for chiral magnetic effect in heavy ion collisions

Chiral magnetic effect (CME) is a macroscopic transport phenomenon induced by quantum anomaly in the presence of chiral imbalance and an external magnetic field. Relativistic heavy ion collisions provide the unique opportunity to look for CME in a non-Abelian plasma, where the chiral imbalance is created by topological transitions similar to those occurring in the Early Universe. The isobar run at Relativistic Heavy Ion Collider was proposed as a way to separate the possible CME signal driven by magnetic field from the background. The first blind analysis results from this important experiment have been recently released by the STAR Collaboration. Under the pre-defined assumption of identical background in RuRu and ZrZr, the results are inconsistent with the presence of CME, as well as with all existing theoretical models (whether including CME or not). However the observed difference of backgrounds must be taken into account before any physical conclusion is drawn. In this work, we show that once the observed difference in hadron multiplicity and collective flow are quantitatively taken into account, the STAR results imply a finite CME signal contribution of about 2%. [ref: 2205.00120]

# Upcoming seminars

June 29, 2022 - Jennifer Rittenhouse West (LBNL) (Host: Xin-Nian Wang) Joint nuclear theory seminar on Wednesday!

This will conclude our 2021-2022 seminar year - we hope everyone has a good summer and will be happy to see you in the fall.

# Previous Seminars this year

### Tuesday, 06.21.2022, 3:30 PM PDT

Dr. Aihong Tang (BNL)

Host: Xin-Nian Wang

Global Spin Alignment in Relativistic Heavy Ion Collisions : A Progress Review

In relativistic heavy ion collisions, quarks can possess global spin polarization in a globally vortical system. Such process is initially induced by the spin-orbital coupling, and the evolution of polarized quarks and the subsequent formation of hadrons involves various interesting physics mechanisms. This phenomena can be studied either by global spin polarization of hyperons or global spin alignment of vector mesons. Recently the STAR collaboration released interesting results of global spin alignment for phi- and K*-mesons. It is found that the surprisingly large value of phi-meson global spin alignment cannot be explained by conventional mechanisms, but can be accommodated by a model invoking the strong force field. In this talk we will review the recent progress in the understanding of global spin alignment, and in particular we will discuss STAR's result and its implications.

### Monday, 06.13.2022, 3:00 PM PDT (Hybrid at Persevervance Hall, note special time and date!)

Prof. Ulrich Mosel (Giessen University)

Host: Jennifer Rittenhouse West

Neutrino-nucleus interactions in quantum-kinetic transport theory

The analysis of results from long-baseline experiments such as T2K, NOvA and DUNE requires knowledge of the incoming neutrino energy. The latter has to be reconstructed from only partially measured final states of the reaction. Any theory thus has to go beyond the calculation of inclusive cross sections and has to deliver the full final state of the reaction. Since all present experiments work with nuclear targets not only the initial, first interaction of the incoming neutrino plays a role. In addition, the final state interactions of the initially produced hadrons with the nuclear environment are important and determine the final state. The state-of-the-art method to treat such processes is quantum-kinetic transport theory which has been around since 50 years, but only over the last 20 years major numerical implementations to describe nuclear reactions have become available. In my talk I will illustrate some of the results obtained with such a theory, applied both to nuclear reactions and neutrino-nucleus reactions.

### Tuesday, 06.07.2022, 12 PM PDT - Special time!

Dr. Sergey Kulagin (Institute of Nuclear Research, RAS Moscow)

Host: Jennifer Rittenhouse West

What can we say about modification of the bound nucleon at the parton level from global QCD fits?

We briefly review available experimental observations on nuclear effects in deep-inelastic scattering (DIS). We then briefly discuss a few basic mechanisms responsible for nuclear corrections and review progress in understanding the observed phenomenon focusing on the valence quark region. We report the results of our global QCD analysis which includes a "standard" set of high-energy data for the proton target (DIS, DY production of lepton pair as well as W+- / Z boson production) and also nuclear 2H, 3H, and 3He DIS data. In this analysis we treat nuclear corrections in DIS in terms of a nuclear convolution approach with off-shell bound nucleon. The off-shell correction describes the modification of parton distributions in bound nucleons, which is determined along with the parton distribution functions (PDFs). A number of systematic studies have been performed aiming to estimate the uncertainties arising from the use of various deuterium data sets, from the model of high twist contributions to the structure functions, from the treatment of target mass corrections. We compare our predictions for the ratio F2n/F2p and the d/u ratio of the quark distributions with the results of other analyses as well as with the recent data from the MARATHON experiment.

### Tuesday, 05.31.2022, 3:30 PM PDT

Dr. Christopher McGinn (Univ of Colorado Boulder)

Inclusive and Electroweak Boson-tagged Jets as Probes of the Quark-Gluon Plasma and Medium Response

Jets, as proxy for hard scattered partons in initial collision of heavy and ultrarelativistic nuclei, are modified significantly relative their vacuum reference counterparts when traversing the subsequently formed hot-and-dense medium of deconfined quarks and gluons known as the Quark-Gluon Plasma (QGP). Specifically, a suppression in the overall production of jets is observed compared to vacuum expectation, as well as a modification to jet fragmentation patterns towards softer fragments. These phenomena are known collectively as 'jet-quenching'. Recently, much attention has been paid to the impact of jet-medium interactions on the medium itself, in searches for medium response and in searches for quenching in small systems (such as proton-nucleus collisions) in the context of observed high-pT v2. Using data taken with the ATLAS detector at the LHC, sqrt(sNN) = 5.02 TeV, jets produced with electroweak boson partners (unmodified by strong-force interactions in QGP) are studied to characterize both the jet production and fragmentation, with the latter providing insight into the necessity of incorporating medium response in theoretical model comparisons. Additionally, simultaneous studies of jet v2 and quenching in big-and-small systems reveals there may be more questions on the exact nature of the jet-medium interactions in both systems and how they lead to the physical final state observed.

### Tuesday, 05/24/2022,3:30 PM PDT

Prof. Mike Lisa (Ohio State University)

Host: Xin-Nian Wang

Subatomic Smoke Rings: Polarization and Toroidal Vorticity in the QGP

Since the discovery of global hyperon polarization in Au+Au collisions at RHIC about five years ago, there has been intense theoretical and experimental focus on the topic. After a brief review, I will discuss novel vortex structures that may be generated in two situations. The first is a p+A collision, which may produce droplets of QGP that develop toroidal vortex ("smoke ring") structure. Experimental observation of such a structure would provide compelling evidence supporting the hydrodynamic nature of this tiny system, a much-debated topic today. The other is an idealized "hot moving spot" that may result from thermalization of a jet in an expanding QGP; in this case, the "smoke ring" centers on the jet direction. In both cases, we suggest an experimental observable to measure the toroidal vortex structure, and present full hydrodynamical simulations to make quantitative predictions, including initial state fluctuation effects. I will mention prospects and challenges for observing this novel phenomenon in experiment.

### Tuesday, 05.17.2022, 3:30 PM PDT

Prof. Jorge Noronha (UIUC)

Host: Xin-Nian Wang

Hydrodynamic Frames: the Good, the Bad, and the Ugly

Three of the most cutting-edge experiments in modern science, RHIC, LHC, and LIGO are now producing data whose description requires a major overhaul of our current understanding of what constitutes fluid dynamic behavior in the relativistic regime. In this talk I will explain how the choice of hydrodynamic variables in a system out of equilibrium, i.e., our definition of the so-called hydrodynamic frame, affects the domain of applicability of relativistic viscous fluid dynamics formulations. I will also show how developments in relativistic viscous hydrodynamics obtained in heavy-ion collisions could be instrumental in determining the viscous properties of ultradense matter formed in neutron star mergers.

### Tuesday, 05.10.2022, 3:30 PM PDT

Prof. Kenji Fukushima (Univ. of Tokyo)

Host: Feng Yuan

Continuity or Discontinuity between Nuclear and Quark Matter and the Astrophysical Implications

In this talk I will review theoretical scenarios of quark matter at high density. Although a phase transition is not logically excluded, a crossover or weak first-order transition is likely to occur. I will explain how the equation of state is constrained by the neutron star observation and demonstrate that the future gravitational wave detection can identify the nature of the quatk matter onset.

### Wednesday, 05.04.2022, 3:30 PM PDT (Special date)

(Hybrid talk in the INPA room)

Prof. Carl Schroeder (LBNL/UCB)

Host: Peter Jacobs

Laser-Plasma Accelerators

Slides

Laser-driven plasma-based accelerators (LPAs) are able to sustain extremely large accelerating gradients, orders of magnitude larger than those achievable using conventional metallic accelerating structures. LPA experiments have demonstrated the generation of multi-GeV electron beams in cm-scale plasmas. These high gradients have attracted interest in LPA technology for high-energy collider applications. In this talk, I will review the basic physics of LPAs, LPA research in the BELLA Center at LBNL, and how LPAs can be developed for various applications. Employing LPAs as a linac for an e+e- collider is the most challenging application, and I will discuss the design considerations and expected performance for an LPA-based linear collider. .

### (This will be a hybrid seminar in theTheory Lounge)

Dr. Jan Steinheimer (FIAS)

Hyper-nuclei production in heavy-on collisions

Hypernuclei have been an interesting topic of study for more than half a century. Yet their properties are still not fully understood. In this talk, I will give a short introduction to hypernuclei and how they can be produced. Here, the production of nuclei with one or more units of strangeness from relativistic heavy ion collisions is of particular interest, due to the abundance of strange baryons created. While the absorption of hyperons offers a chance to create large hypercluster in the spectator fragments of nuclear collisions, also the observation of light hypernuclei from the central hot region is of interest. I will discuss how the production probability can be well described by a coalescence mechanism using the UrQMD model over a beam energy range of three orders of magnitude. In addition I will show how the measurement of different nuclei can be used to determine the size of the region of homogeneity from which baryons, that will eventually form (hyper-)nuclei, are emitted . Within this context I will discuss recent interpretations of the centrality dependence of (hyper-)nuclei production.

### Tuesday, 04.19.2022, 3:30 PM PDT

Dr. Brandon Kriesten (Center for Nuclear Femtography)

Host: Jennifer Rittenhouse West

Quark and Gluon Spatial Distributions in the Nucleon

Studying the role of gluonic observables in exclusive scattering processes is essential as new physics programs, such as an electron ion collider, are planned in unprecedented kinematic regimes. I will present a parameterization of quark and gluon generalized parton distributions (GPDs) calculated using a reggeized spectator model. This parameterization is constrained using a combination of lattice QCD form factor calculations and extracted deep inelastic parton distributions. We evolve our parameterization at leading order in Q2 to the scale of experimental data using a perturbative QCD evolution framework. We demonstrate expected spatial distributions under Fourier transformation using our parametrization. Understanding the behavior of gluon GPDs is a first step towards extracting the gluon contribution to deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) observables at the EIC.

### Tuesday, 04.12.2022, 3:30 PM PDT

Dr. Gunther M Roland (MIT)

Hot QCD with sPHENIX at RHIC

Over the last decades heavy-ion experiments at RHIC and LHC have demonstrated a range of novel QCD phenomena that emerge under conditions of extreme pressure and temperature. New efforts, sPHENIX at RHIC and the upgraded LHC experiments, will begin collecting high precision new data in the next year. These data will allow us to investigate the microscopic origins of observed phenomena in the produced Quark-Gluon Plasma (QGP). Of particular importance will be the complementarity of experiments in the two energy regimes, elucidating the temperature dependence of QGP properties. In this talk I will present the sPHENIX design, construction status and expected performance, and discuss case studies that illustrate key aspects of the sPHENIX physics program.

### Tuesday, 03.29.2022, 3:30 PM PST

Prof. MaElena Tejeda Yeomans (Universidad de Colima)

Host: Jennifer Rittenhouse West

Rise and Fall of Lambda and anti-Lambda Polarization from the Core-Corona Model

The polarization of particles produced in heavy-ion collisions provides the perfect arena to study amazing phenomena such as the collective rotation of the nuclear medium, the transference of global angular momenta to spin properties of certain particles, and the evolution of these properties when there are drastic changes in the properties of the hot and dense medium. Recently, measurements by STAR collaboration at RHIC and HADES collaboration at GSI show the rising of Lambda and anti-Lambda global polarization with decreasing collision energy. Many models predict the vanishing of global polarization due to the lack of system angular momentum, but the height and location of the expected peaks for both Lambda and anti-Lambda are still not well understood. In this talk I will report on recent work to study Lambda and anti-Lambda global polarization in heavy-ion collisions using the core-corona model, where the source of these hyperons is a high-density core and a less dense corona. I will show that the overall properties of the polarization excitation functions can be linked to the relative abundance of Lambdas and anti-Lambdas coming from the core versus those coming from the corona. We will see how the global polarization peak at the expected ranges of collision energies but, the exact positions and heights of these peaks depend on the centrality class, which is directly related to the QGP volume and lifetime, as well as on the relative abundances of Lambdas and anti-Lambdas in the core and corona regions. Finally, I will talk about the improvements we are making to this model to study polarization properties of other species, and as a probe of critical phenomena in the nuclear medium.

### Tuesday, 03.22.2022, 3:30 PM PST

Dr. Xiaojun Yao (MIT)

Host: Xin-Nian Wang

Pure quark and gluon jet observables

Disentangling quark- and gluon-initiated jets can help us to better understand fundamental interactions in QCD and use jets as probes of the quark-gluon plasma in heavy ion collisions. Many previous studies relied on the Sudakov factors of some jet substructure observables such as the soft drop jet mass in the tail region and failed to reach a 100% efficiency in the disentangling. In this talk, I will introduce novel jet observables that are made pure quark or gluon in a wide kinematic region. The construction is based on the collinear drop grooming technique and nonperturbative effects are taken into account. I will show both analytic and Monte Carlo results for these observables in proton-proton collisions and discuss the impact of initial-state radiation and multi-parton interaction. Finally, I will discuss the potential obstacles in applying these observables in heavy ion collisions.

### Tuesday, 03.15.2022, 2:00 PM PST (Special time)

Dr. You Zhou (NBI)

Host: Xin-Nian Wang

Multi-particle correlations for the new decade of QGP studies

Multi-particle correlations have been compelling tools to probe the properties of the Quark-Gluon Plasma (QGP) created in the ultra-relativistic heavy-ion collisions. In this seminar, I will present a generic recursive algorithm for multi-particle cumulants, which enables the calculation of arbitrary order multi-particle cumulants. Among them, I will emphasize a particular series of mixed harmonic multi-particle cumulants, which measures the general correlations between any moments of different flow coefficients. The study of these new multi-particle cumulants in heavy-ion collisions will significantly improve the understanding of the initial event-by-event geometry fluctuations and the hydrodynamic response in the final state. This will pave the way for more stringent constraints on the initial state and help extract more precise information on how the created hot and dense matter evolves. Last but not least, I will show the most recent study of correlations between anisotropic flow and mean transverse momentum in terms of multi-particle correlations/cumulants. I will show how we can directly access the initial conditions of heavy-ion collisions using the latest experimental measurements at the LHC and discuss the critical challenge of the state-of-the-art QGP studies via Bayesian analyses.

### Tuesday, 03.08.2022, 2:00 PM PST

Dr. Giuliano Giacalone (Heidelberg University)

Host: Xin-Nian Wang

The initial state of the quark-gluon plasma: status, prospects, interdisciplinary connections

The hydrodynamic model of the quark-gluon plasma (QGP) formed in relativistic nuclear collisions has permitted us over the years not only to obtain quantitative estimates of the transport properties of this medium from data, but also to establish a phenomenologically viable picture of its initial condition and how it emerges from the interaction of two ions at high energy. I review the current understanding of the initial condition of the QGP, emphasizing the outcome of state-of-the-art models and the overall picture that they yield. I discuss the progress made in the definition of observable quantities that offer a specific sensitivity to the physics of the initial state, with a focus on recent results (both theoretical and experimental) on mean transverse momentum-anisotropic flow correlations. Such observables pose unprecedented constraints on the parameters of state-of-the-art Monte Carlo generators for nuclear collisions, demonstrating, in particular, the importance of having an accurate implementation of the structure of the colliding ions, and the nucleons therein, in such frameworks. Consequently, the initial state of heavy-ion collisions provides fertile ground for new interdisciplinary connections involving different aspects of hadronic and nuclear physics across energy scales.

### Spin-momentum correlation in hot and dense QCD matter

The transport phenomena involving spin are instrumental in investigating quantum effects in many-body systems. In heavy-ion collisions, the recent measurement of spin polarization and spin alignment opens a new avenue to explore the properties of hot and dense QCD matter. Based on linear response theory and quantum kinetic equation, we have systematically studied spin-momentum correlation induced by hydrodynamic gradients [1]. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear [2]. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. The possible signature of SIP at RHIC and LHC will be elaborated. Then, I will present our prediction for the signature Spin Hall effect induced by baryon chemical gradient at RHIC beam scan energies [3,4]. If time permitted, I will briefly discuss the effect of SIP on vector mesons. .

### 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

### Host: Aaron Meyer

Lattice QCD Determination of the Bjorken-$x$ Dependence of PDFs at Next-to-next-to-leading Order

The large-momentum effective theory (LaMET) is a systematic approach to calculate parton physics from Euclidean approaches such as lattice QCD. With major progress in the lattice renormalization and perturbative matching, the lattice calculation of PDFs with LaMET is now entering the stage of precision control. In this talk, I will present a state-of-the-art lattice QCD calculation of pion valence quark distribution with next-to-next-to-leading order matching correction, which is done using two fine lattices with spacings $a=0.04$ fm and $0.06$ fm and valence pion mass $m_\pi=300$ MeV at boost momentum as large as 2.42 GeV. I will demonstrate that perturbative matching in Bjorken-$x$ space yields a reliable determination of the valence quark distribution for moderate x with a target precision, which shows considerably improved systematic uncertainty compared to a previous analysis of the same lattice data with a short-distance factorization approach in the coordinate space, and is in excellent agreement with the most recent global analyses.

### Tuesday, 2022.01.25, 3:30 PM PST

Prof. Rene Bellwied (University of Houston)

Matter under extreme conditions - Particle Collisions along the QCD Phase Diagram

Relativistic particle collisions have come a long way during the past two decades with the characterization of states of matter along the QCD phase transition line. I will try to show how these discoveries lead to significant multi-disciplinary efforts to understand the creation and evolution of matter under extreme conditions. Examples that will be highlighted are the connection of fundamental quantum theories to collective phenomena and particle production, as well as astrophysical measurements that link to interactions observed at RHIC and LHC.

### Tuesday, 2022.01.18, 3:30 PM PST

Prof. Tanja Horn (JLab & The Catholic University of America)

Host: Jennifer Rittenhouse West

PION AND KAON STRUCTURE FUNCTIONS