Bulletin of the American Physical Society
6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023; Hawaii, the Big Island
Session C13: Relativistic Heavy Ions I (Hard probes) |
Hide Abstracts |
Chair: Anthony Timmins, University of Houston Room: Hilton Waikoloa Village Kona 2-3 |
Tuesday, November 28, 2023 7:00PM - 7:15PM |
C13.00001: Probing Quark-Gluon Plasma with Large Radius Jets with ATLAS Berenice Garcia Quark-Gluon Plasma (QGP) is a unique state of matter where quarks and gluons, normally confined within hadrons like protons and neutrons, move collectively as a low-viscosity liquid. The QGP is created through high-energy collisions of heavy-ions at relativistic speeds and jets, high collimated sprays of particles, can be used as probes to explore its properties. The ATLAS experiment at the Large Hadron Collider (LHC) has collected Pb+Pb 2018 and proton-proton 2017 data, which can be used to examine the radiation and fragmentation patterns of particles within jets. The main focus of this talk is the inclusive jet nuclear modification factor ($mathrm{R_{AA}}$), which quantifies the energy loss of jets in heavy-ion collisions compared to vacuum conditions. For the first time in ATLAS heavy-ion data, this analysis explores the energy distribution within a jet radius by comparing $mathrm{R_{AA}}$ values for jets with different radii (R=1.0 and 0.4). The performance and status of the measurement with R=1.0 jets will be discussed. |
Tuesday, November 28, 2023 7:15PM - 7:30PM |
C13.00002: Interpretable Machine Learning applications to Jet Background Subtraction Tanner A Mengel, Charles P Hughes, Patrick J Steffanic, Antonio C da Silva, Christine E Nattrass Jet measurements can provide constraints on the properties of the quark gluon plasma, but the kinematic reach is limited by the large, fluctuating background. Previous applications of machine learning to jet background subtraction have shown improvements over the traditional background subtraction methods, especially at low jet momentum. While machine learning applications generally lead to improvements, care must be taken to ensure they are not at the cost of interpretability and bias from models used for training. We present a novel application of symbolic regression to extract a functional representation of a deep neural network trained to subtract background for measurements of jets. With this functional representation we show that the relationship learned by a neural network is approximately the same as a new background subtraction method using the particle multiplicity in a jet. This multiplicity method uses measured features, rather than learned weights, to achieve most of the improvements demonstrated by the deep neural network. Additionally, we show the algorithmic complexity of the deep neural network can be decreased by reducing it to a shallower representation while still achieving similar performance. Our study demonstrates that interpretable machine learning methods can provide insights into underlying physical processes and achieve the performance of black-box machine learning without the opaqueness and model bias. |
Tuesday, November 28, 2023 7:30PM - 7:45PM |
C13.00003: Fully-Reconstructed Jet Invariant Cross Sections and RpPb at √sNN = 8 TeV Using the ALICE Detector Austin Schmier Measurements in small systems such as pp and p–Pb collisions are important in order to provide constraints on nuclear PDFs and disentangle initial and final state effects, including cold nuclear matter effects and modifications due to the presence of a medium in heavy ion collisions. While such a medium is not expected in small collision systems, recent studies still suggest the presence of collectivity. The fully-reconstructed jet invariant cross sections and nuclear modification factor (RpPb) for different jet radii are presented from measurements using the ALICE detector at the CERN LHC in pp collisions at √s = 8 TeV and p–Pb collisions at √sNN = 8.16 TeV. For this analysis, jets are reconstructed using charged tracks from the Time Projection Chamber (TPC) and the Inner Tracking System (ITS), and neutral constituents from clusters in the Electromagnetic Calorimeter (EMCal). |
Tuesday, November 28, 2023 7:45PM - 8:00PM |
C13.00004: Simultaneous description of jet quenching and asymmetry in heavy-ion ion collisions Ron A Soltz The study of jet quenching in heavy-ion collisions is a top active experimental and theoretical investigation. We apply Bayesian techniques to test simple parameterizations of jet quenching and asymmetry in Pb+Pb collisions at the LHC, and experimental measurements of these quantities are used to constrain the mean and rms-width of the energy loss distributions. These parameterizations are also used to study the explore assumptions regarding various forms of correlated errors for each observable. Impacts for future experimental analyses and theoretical models will be discussed. |
Tuesday, November 28, 2023 8:00PM - 8:15PM |
C13.00005: Classifications of quark/gluon and quenched jets using machine learning technique for high energy heavy ion collisions Taketo Yokoo In Quantum Chromodynamics, quarks and gluons carry different color charges which lead to different properties of jets. In particular, it is predicted that the energy loss due to the interaction between parton and Quark-Gluon Plasma (QGP) is different for quarks from that for gluons. In order to validate this prediction, it is necessary to distinguish accurately jets originally from quarks (quark jets) from those from gluons (gluon jets). However, the differences between these jets are subtle, making it difficult to distinguish them based on current approaches. Therefore, a machine learning (ML) approach utilizing multivariate analysis is applied. In this study, JETSCAPE[1] framework including parton energy loss is used to study the validity of ML for the jet identification in proton-proton and heavy ion collisions. In this talk, the current status of quenched jet classification for quarks and gluons will be reported. |
Tuesday, November 28, 2023 8:15PM - 8:30PM |
C13.00006: Particle production as a function of underlying-event activity in pp, p-Pb, and Pb-Pb collisions and search for jet-like modifications with ALICE Omar Vazquez Rueda In this contribution, the similarity between small and large collision systems will be further explored using the underlying event (UE) charged-particle density, NT and the self-normalized version, RT. By selecting on NT or RT and topological region, different microscopic processes contributing to the inclusive production can be isolated. |
Tuesday, November 28, 2023 8:30PM - 8:45PM |
C13.00007: Dielectron production in high-multiplicity pp collisions at $sqrt{s}$ = 13 TeV with ALICE Hikari Murakami Dielectron production is a powerful tool to investigate the properties of the quark-gluon plasma created in relativistic heavy-ion collisions, as they carry information about the temperature of the medium and its space-time evolution without any distortion due to final-state interactions. Dielectron measurements in pp collisions serve as reference for heavy-ion studies since no medium effect is expected. |
Tuesday, November 28, 2023 8:45PM - 9:00PM |
C13.00008: Recent results on Upsilon meson production in PbPb collisions with CMS. Manuel Calderon de la Barca Sanchez One of the fundamental aspects of the formation and interaction of heavy-quark bound states in the quark-gluon plasma is amount of their suppression, expected to be stronger with quarkonia with smaller binding energies. Past results show a significant suppression of Upsilon(1S) mesons in heavy ion collisions, with Upsilon(2S) mesons being even more suppressed. However, for the Upsilon(3S) meson, only upper limits had been reported. In this talk, we report on the observation of the Upsilon(3S) meson and the recent studies of the production of Upsilon mesons in lead-lead collisions reported by CMS. For the first time, the nuclear modification factor has been extended to the Upsilon(3S) state, which is the most strongly suppressed meson measured to date. The results are compared with model calculations describing the dynamics of quarkonia in a hot environment. Relevant Upsilon results from pPb collisions in CMS will be discussed as well. |
Tuesday, November 28, 2023 9:00PM - 9:15PM |
C13.00009: Performance Study on High Level Trigger for Vector Boson Fusion Process in CMS Run 3 Data at √s = 13.6 TeV Raymond Kil The Compact Muon Solenoid (CMS) comprises a two-level trigger system that selects and stores potentially interesting proton-proton collision events in light of reducing a large fraction of well-known background and efficiently managing the data produced at the Large Hadron Collider (LHC). This poster presents a study on the online High Level Trigger (HLT) system at CMS and its event selection performance on Vector Boson Fusion (VBF) Higgs production mechanism in Run3 of the LHC in the year of 2023 with integrated luminosity of 13 fb−1. Specifically, the efficiency study is done on the recently introduced event-level trigger paths1 characterized by the dijet invariant mass mjj and the relative pseudorapidity ∆η criteria of multijet events. 2023 Run3 SingleMuon datasets are employed with kinematic cuts applied on the transverse momentum of leading and sub-leading jets (pT1, pT2), mjj , and ∆η matching the trigger path algorithm, as well as calorimeter energy fractions and muon property cuts for well-defined event selection. With selected offline reconstructed events serving as the baseline, efficiency is obtained by taking the ratio of the number of events captured by VBF trigger paths to that of offline reconstructed events that are ideally accepted by the trigger path. Accurate and efficient performance of HLT on VBF trigger path will facilitate both the Standard Model studies and Beyond Standard Model (BSM) searches including Soft Unclustered Energy Pattern (SUEP) process. |
Tuesday, November 28, 2023 9:15PM - 9:30PM |
C13.00010: Asymmetric Jet Broadening and the RAA x v2 Puzzle Joseph Bahder, Hasan R Rahman, Matthew D Sievert For decades, a coupled description of the nuclear modification factor (RAA) and anisotropic flow (vn) of hard particles in relativistic heavy ion collisions that are theorized to generate Quark Gluon Plasma (QGP), especially at the Large Hadron Collider (LHC), has been an enduring challenge in the field. Many attempts have made substantial strides in effectively modeling RAA and the generation of anisotropic flow for very hard particles (pT > 10 GeV), however the anisotropic flow of low-pT (1 GeV < pT < 10 GeV) hard particles has been dramatically underpredicted by all models based on first principles perturbative QCD calculations of jet-medium interactions including energy loss and symmetric momentum broadening. We discuss the phenomenological effect of the emerging class of asymmetric jet-broadening effects coupling to the QGP flow and gradients of flow and temperature on jet anisotropic flow, showing that these effects are integral to a fully coupled description of RAA and vn. |
Tuesday, November 28, 2023 9:30PM - 9:45PM |
C13.00011: Non-Perturbative Transport of Heavy Quarkonia in Ultra-Relativistic Heavy-Ion Collision Biaogang Wu, Zhanduo Tang, Ralf F Rapp Ultra-Relativistic Heavy-Ion Collisions (URHICs) provide a fertile ground for studying Quantum Chromodynamics (QCD) under extreme conditions. The heavy quarks and quarkonia provide an excellent probe of the medium created during such collisions, through the use of pertinent transport models. A central input to quarkonium transport models are their reaction rates in the thermal medium. To date, these have mostly been calculated using perturbative QCD. However, non-perturbative effects within the strongly coupled quark-gluon plasma (sQGP) are likely of prime importance. |
Tuesday, November 28, 2023 9:45PM - 10:00PM |
C13.00012: Axial anomaly effect to the chiral-partner structure of diquarks at high temperature Daiki Suenaga, Makoto Oka Masses of positive-parity and negative-parity diquarks are investigated at finite temperature with a quark chemical potential. We employ the three-flavor Nambu-Jona-Lasinio model, in order to delineate chiral properties of the diquarks, in particular, the mass degeneracy of chiral partners under extreme conditions. We focus on the effects of $U(1)_A$ axial anomaly on manifestation of the chiral-partner structures. We find that, in the absence of anomaly effects to the diquarks, the mass degeneracies in all $[ud]$, $[su]$ and $[sd]$ diquark sectors take place prominently above the pseudocritical temperature of the chiral restoration. On the other hand, the anomaly effects are found to hinder the $[ud]$ diquark from exhibiting the mass degeneracy, accompanied by a slow reduction of the $ar{s}s$ condensate, while the $[su]$ and $[sd]$ diquarks are not much affected. Our present investigation will provide useful information on the chiral-partner structure with the anomaly effects of diquarks for heavy-ion collision experiments of singly heavy baryons and doubly heavy tetraquarks, and for future lattice simulations of the diquarks. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700