10/10/2023

Measurements of deuteron-correlations in √s_NN = 3 GeV Au+Au collisions at the STAR experiment

Yu Hu, Lawrence Berkeley National Laboratory
2:00 PM Tuesday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

Heavy-ion collisions provide a unique opportunity to explore nucleon-hyperon (N-Y) interactions, primarily through two-particle correlations. The d-Λ correlations shed light on both N-Y two-body and N-N-Y three-body interactions, which is crucial for understanding neutron star properties. We present the first measurement of d-Λ correlation with √s_NN = 3 GeV Au+Au collisions at STAR. Using the Lednicky-Lyuboshitz formalism, we characterize emission source size, the scattering length, and the effective range of d-Λ interactions. The extracted parameters will be compared to those from p-Λ correlations. The physics implications on final state interactions involving hyperons and the hypertriton inner structure will also be discussed.

09/19/2023

Baryon number transport at RHIC and EIC

Zhangbu Xu, Brookhaven National Laboratory
11:00 AM Tuesday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

Baryon number (B) is a conserved quantum number that prevents protons (B = 1) and stable nuclei from disintegration and governs the visible Universe as it is today. It is conventionally assumed that the unit baryon number in a nucleon is distributed equally among its three valence quarks. An alternative picture was proposed at the birth of the theory of the Quantum Chromodynamics (QCD) half a century ago that the baryon number is instead traced by the baryon junction, a non-perturbative Y-shaped topology of gluons that is connected to all three valence quarks. Neither of these pictures has been experimentally verified. I will present the three experimental results we carried out at RHIC recently to test the hypotheses using isobar and BES-II data collected by the STAR Collaboration. I will also review the previous experimental measurements in lepton+hadron and p+p collisions relevant to this topic, and discuss what we can do in the future at RHIC and EIC.

09/11/2023 - 09/15/2023

50 Years of Quantum Chromodynamics

Luskin Conference Center

06/12/2023

Comparing the MARTINI and CUJET models for jet quenching

Shuzhe Shi, Tsinghua University
9:00 AM Monday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

Jets produced by the initial hard scattering in heavy ion collision events lose energy due to interactions with the color-deconfined medium formed around them: The quark-gluon plasma (QGP). Jet-medium interactions constitute an important theoretical and experimental field for studies of QGP, and various models with different assumptions have been proposed to describe them. A fair and direct comparison of these models requires that all other aspects of the simulation be fixed, which is achieved in this work by relying on the jetscape framework. We employ jetscape to directly and comprehensively compare two successful energy loss models: cujet and martini. We compare the models with the results of measurements of jet spectra and substructure observables. With the strong coupling tuned separately, we find that the two models broadly agree with each other in nuclear modification factors for charged hadrons and jets with cone size R = 0.4. Systematic differences are reported in fragmentation functions, jet shape, and cone-size dependent jet RAA. Photon observables will also be discussed.

05/30/2023

Quantum algorithms for Hamiltonian simulation of non-Abelian interactions

Jesse Stryker, University of Maryland
9:00 AM Tuesday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

Despite their many successes, the established methods of calculation in lattice quantum chromodynamics (QCD) break down or have limited applicability for various scenarios of interest as a result of sign problems in the Monte Carlo simulations. Quantum simulation has been identified as a way to circumvent such sign problems, but the computational framework is vastly different and its application remains largely unexplored in this context. The arrival of functional quantum computers has therefore created a deficit of algorithmic protocols suitable for leveraging said devices to study gauge theories such as QCD. In this talk, I present our recently developed quantum algorithms for time evolution of a 1+1-dimensional SU(2) gauge theory - a stepping stone on the way to strong interactions in the Standard Model. We take advantage of the structure of the Hamiltonian's interactions while remaining sufficiently general that the methods could be adapted to QCD. As examples, the Schwinger-boson and loop-string-hadron formulations of the theory are analyzed in depth, with the latter being found to provide substantial gate-count savings.

05/03/2023

Three-dimensional nucleon structure

Alexei Prokudin, Penn State Berks and Jefferson Lab
11:00 AM Wednesday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

I will discuss the three-dimensional (3D) nucleon structure encoded in the Transverse Momentum Dependent distributions, providing an overview of the current knowledge. Using several examples, I will demonstrate the significance of the 3D structure and its relation to other topics in hadronic physics.

05/01/2023

Systematic Calculation of PDFs and GPDs from Lattice QCD

Xiang Gao, Argonne National Laboratory
9:00 AM Monday, online ZOOM

Parton distribution functions (PDFs) and generalized parton distribution functions (GPDs) are fundamental quantities that encode information about the quark and gluon structure of hadrons. While PDFs have been extensively studied in experiments and phenomenological models, GPDs are still poorly known due to their challenging experimental access. With years’ development of quasi-PDFs approaches, the lattice QCD can now provide a systematic framework to compute these quantities from first principles. In this talk, we discuss some recent results of x-dependent quark PDFs and GPDs, as well as the first few moments, obtained from lattice calculations.

04/17/2023

Harmonics of Parton Saturation in Lepton-Jet Correlations at the EIC

Xuan-Bo Tong, The Chinese University of Hong Kong
9:00 AM Monday, online ZOOM

Parton saturation is one of the most intriguing phenomena in the high-energy nuclear physics research frontier, particularly as the Electron-Ion Collider (EIC) era approaches. Various observables have been proposed to search for signals of parton saturation at the EIC, with two-particle correlations emerging as a promising choice. In this talk, I will present our recent work (arXiv:2211.01647) on lepton-jet correlation and its application in saturation physics. Using the color glass condensate framework, we show that the azimuthal angle anisotropies of lepton-jet correlation are sensitive to the saturation momentum strength in the EIC kinematic region. Unlike the predictions of collinear framework calculations,  we observe significant nuclear modification of the anisotropies in comparisons of the saturation-framework results in e + p and e + Au scatterings. This new observable has the potential to provide compelling evidence for parton saturation at the upcoming EIC.

04/13/2023

Transverse polarization phenomena and new jet substructures

Zhite Yu, Michigan State University
10:00 AM Thursday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

Transverse polarization phenomena on high-energy hadron colliders such as the LHC give rise to novel observables originating from the quantum interference of distinct helicity states. These observables offer insights into hard scattering processes that complement cross-section data and can serve as crucial probes for potential new physics, particularly CP-violating interactions, but have been relatively underexplored. This talk will concentrate on the linear polarization of vector bosons, encompassing both massive vector bosons like W+/- and massless vector bosons such as gluons. The production of such polarization in high-energy colliders manifests as novel jet substructures, characterized by azimuthal energy deposition asymmetries within the transverse jet plane. Analyzing these observables can help test the Standard Model at a unique level and offer innovative tools for the discovery of new physics.

04/03/2023

Quantum AI: From near-term to fault-tolerance

Junyu Liu, University of Chicago
9:00 AM Monday, online ZOOM

Quantum machine learning, namely, running machine learning algorithms on quantum devices, has been considered a flag-ship application of quantum computing. In this talk, we will describe two perspectives of quantum machine learning: near-term algorithms and fault-tolerant algorithms. In the near-term realizations, I will discuss applications of variational quantum circuits in machine learning problems, and how a theory of quantum neural tangent kernel could be an analytic principle to optimize quantum neural networks. In the fault-tolerant realizations with quantum error correction, I will briefly discuss some ongoing works with end-to-end applications of the HHL algorithm that provides a provable, generic quantum advantage to a class of machine learning problems. Our works show that fundamental physics research, such as chaos and dissipation, could be helpful for important and timely problems of machine learning algorithm designs from scientific research to the industry.

03/23/2023

Machine learning for sign problems

Yukari Yamauchi, Institute for Nuclear Theory at the University of Washington
12:30 PM Thursday, online ZOOM

Sign problems in lattice QCD prevent us from non-perturbatively calculating some important properties of dense nuclear matter both in and out of equilibrium. In this talk, I will discuss numerical methods to alleviate these sign problems in lattice field theories: complex normalizing flows and subtractions. Both of the methods are the cousins of the so-called manifold deformation method, in which one deforms the manifold of integration in the path integral to the complex plane, aiming for a milder sign problem. I will demonstrate the method of complex normalizing flows with the ϕ⁴ scalar field theory at complex coupling. The subtraction method will be demonstrated with the Thirring model at finite density, which possesses a fermion sign problem.

03/13/2023

Probing hadronization with flavor correlations of leading particles in jets

Yang-Ting Chien, Georgia State University
11:00 AM Monday, Hybrid (Knudsen Hall 5-142 and online ZOOM)

I will discuss nonperturbative flavor correlations between pairs of leading and next-to-leading charged hadrons within jets at the Electron-Ion Collider (EIC). We introduce a charge correlation ratio observable rc that distinguishes same- and opposite-sign charged pairs. Using Monte Carlo simulations with different event generators, rc is examined as a function of various kinematic variables for different combinations of hadron species, and the feasibility of such measurements at the EIC is demonstrated. I will also discuss the correlation between leading hadrons and leading subjets which encodes the transition between perturbative and nonperturbative regimes. The precision hadronization study we propose will provide new tests of hadronization models and hopefully lead to improved quantitative, and perhaps eventually analytic, understanding of nonperturbative QCD dynamics.

03/09/2023

Unraveling the 3D Structure of Nucleon

Yuxun Guo, University of Maryland
1:00 PM Thursday, online ZOOM

Nucleon 3D structure has been one of the most important goals in modern nuclear physics, which will provide, among other insights, an intuitive understanding of how the fundamental properties of the nucleon, such as its mass and spin, arise from the underlying quark and gluon degrees of freedom. In this talk, I will discuss how to study the 3D structure of nucleon via generalized parton distributions (GPDs) with inputs from experiments, lattice and global fits. I will discuss various exclusive measurements at HERA, JLab that can be used to probe the nucleon 3D structures as well as progresses in lattice QCD calculation related to nucleon 3D structures. I will also introduce a global analysis program that combines both experiment and lattice inputs and generate the state-of-art GPDs, which will sheda refreshing new light on the problem of proton structure and confinement.

02/23/2023

High-energy QCD for Higgs and heavy-flavor physics

Francesco Giovanni Celiberto, ECT*
12:15 PM Thursday, online ZOOM

Novel opportunities in the exploration of the dynamics of fundamental interactions at new-generation colliders herald the dawn of a new era for particle physics. Accessing kinematic sectors so far uncharted will open us a window of opportunities to make benchmarks of the Standard Model (SM) as well as (in)direct searches for deviations from SM predictions. Important challenges inside the SM come from the sector of strong interactions. Here, the duality between perturbative and nonperturbative aspects of Quantum Chromodynamics (QCD) leads to yet unresolved puzzles in the answer of fundamental questions, such as the origin of hadrons’ mass and spin, as well as the behavior of QCD observables in relevant kinematic corners of the phase space. In the high-energy regime, the enhancement of energy logarithms due to diffractive semi-hard final states spoils the convergence of the perturbative series in the QCD running coupling. This calls for an improvement of the pure collinear factorization that ac- counts for an all-order resummation of these large logarithmic contributions. We will present recent phenomenological analyses on rapidity, transverse-momentum and azimuthal-angle differential distri- butions sensitive to the inclusive emission in proton collisions of a Higgs boson or/and a heavy-flavored hadron. Our observables are calculated within the hybrid high-energy and collinear factorization, where the standard NLO collinear description is supplemented by the t-channel resummation of energy loga- rithms in the NLL BFKL accuracy. The fair stability that these distributions exhibit under higher-order corrections and scale variations paves the way toward precision studies of high-energy QCD, where the hybrid factorization could serve as a common basis for the development of a multilateral formalism that combines together different resummation mechanisms and matches them with the collinear factorization.

02/09/2023

Thermalization of a hard parton in a QCD plasma

Ismail Soudi, Wayne State University
12:00 PM Thursday, online ZOOM

In heavy ion collisions, hard particles created at the beginning stages must pass through the Quark-Gluon Plasma (QGP) before reaching the detector. As they interact with the medium, these particles experience an energy cascade that transfers energy from the hard scales to the soft medium scales. The primary mechanism of energy degradation for these hard partons is through collinear radiation. However, I will demonstrate how the energy that reaches the soft scales is rapidly transported to large angles with respect to the jet axis, particularly when the opening angle exceeds 0.3 radians. This increased sensitivity to thermalization effects highlights the importance of studying jet cone dynamics in order to fully understand medium response [1-2]. Additionally, I will explore how interactions with the medium can drastically alter the baryon content of jets, resulting in a ring of fermions surrounding the hard core and may contribute to observed baryon enhancements at intermediate transverse moment a[3]. [1]- Schlichting S, Soudi I. JHEP 07:077 (2021) [2]- Mehtar-Tani Y, Schlichting S, Soudi I. arXiv:2209.10569 (2022) [3]- Sirimanna C, Soudi I, Vujanovic G, Xing WJ, Cao S, Majumder A. arXiv:2211.15553 (2022)

01/27/2023 - 01/28/2023

2023 California EIC Consortium Collaboration Meeting

Physics and Astronomy Building, Conference Room 3-326

01/26/2023

Factorization enabling lattice calculation of TMDs

Stella Schindler, MIT
12:00 PM Thursday, online ZOOM

Transverse momentum distributions (TMDs) encode the three-dimensional momentum structure of quarks and gluons inside hadrons. Global fits to experimental data exhibit large uncertainties for non-perturbative parton momenta, a kinematic region where lattice QCD is typically well-positioned to provide complementary information. Unfortunately, TMD dynamics are dominated by the lightcone, which induces a so-called sign problem, an obstacle to numerics that is NP-hard in the general case. To circumvent this issue, lattice theorists typically project Wilson lines appearing in TMD matrix elements from a lightcone path onto an equal-time slice. We derive a factorization formula connecting the resulting lattice-calculable equal-time distributions (quasi-TMDs) to the TMDs that appear in cross-sections (Collins scheme). This formula holds at leading power to all orders in α_s, for all spins and parton flavors. The factorization establishes that lattice and physical TMDs share the same IR physics, and opens the path towards computing gluon TMDs.