Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session QH: Ultrarelativistic Heavy Ions III |
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Chair: Niseem Abdelrahman, University of Illinois Chicago Room: Whittier |
Thursday, October 14, 2021 11:30AM - 11:42AM |
QH.00001: Accessing the Equation of State from Heavy-Ion Data: A Deep-learning Approach Joseph D Lap One of the main goals of the heavy-ion collision research programme is a deeper understanding of the quark gluon plasma (QGP) – the state of matter consisting of a free collection of quarks and gluons. We do not access it directly, however, but rather probe its properties via the kinematic data of particles detected post-hadronization. A major difficulty, then, is extracting the thermodynamic properties of the QGP based on kinematic data. Recently Pang, et al. were able to use a convolutional neural network (CNN) to determine said thermodynamic properties from hydrodynamic simulations of final-state particle distributions in transverse momentum (pT) and azimuthal angle (ɸ). In determining from kinematic data whether the equation of state is first-order or a crossover, one can probe the phase diagram of the QGP in search of the QCD critical point that separates the first-order and crossover regimes. We attempt to extend this work, considering novel architectures, sources of data, and methods of network interpretability. |
Thursday, October 14, 2021 11:42AM - 11:54AM |
QH.00002: QCD Dynamical Properties from Holographic Black Holes Valerio Joaquin J Grefa Jumbo, Jorge Noronha, Jacquelyn Noronha-Hostler, Israel Portillo Vazquez, Claudia Ratti, Romulo Rougemont By using gravity/gauge correspondence, we employ an Einstein-Maxwell-Dilaton model to compute the dynamical properties of a baryon rich quark-gluon plasma. The family of 5-dimensional holographic black holes, which are constrained to mimic the lattice QCD equation of state at zero density, is used to investigate the temperature and baryon chemical potential dependence on the bulk and shear viscosities, baryon charge transport coefficients, and energy loss of light and heavy quarks with a particular focus on the behavior of these observables on top of the critical end point and the line of first order phase transition predicted by the model. |
Thursday, October 14, 2021 11:54AM - 12:06PM |
QH.00003: Fractional Momentum Loss to Discriminate Between Quark and Gluon Energy Loss in the QGP Megan E Connors, Dading Chen Quark Gluon Plasma (QGP), a state of matter that consists of deconfined quarks and gluons, is created in heavy ion collisions. Studying the QGP is vital for a full understanding the strong interactions between subatomic particles. An important probe of the QGP is a jet which is a collimated spray of particles resulting from an energetic quark or gluon produced at the initial stage of the heavy-ion collision. Jets are modified by the QGP due to the interactions and energy loss experienced by their parent partons as they traverse the medium. The fractional momentum loss (Sloss ≡ δpT /pT) can be measured to quantify the energy loss in the QGP by comparing spectra measured in heavy-ion collisions to spectra from p+p collisions. The PHENIX collaboration previously measured Sloss of high-transverse momentum hadrons measured in various collisions systems and energies. In this talk, we will present the fractional momentum loss for reconstructed jets in Pb+Pb collisions at 2.76 TeV in various rapidity ranges using data published by the ATLAS experiment at the Large Hadron Collider. Measuring Sloss for jets from different rapidity ranges may be sensitive to the differences in energy loss expected for quark and gluon jets which would further our understanding of energy loss in the QGP. |
Thursday, October 14, 2021 12:06PM - 12:18PM |
QH.00004: Title : Validation of Glauber model in centrality determination for small systems. Niveditha Ramasubramanian The initial motivation to study d+Au collision was to decouple the effects of cold nuclear matter effects in nuclear modification factor (RAA) in heavy ion collision and use this as a control experiment. |
Thursday, October 14, 2021 12:18PM - 12:30PM |
QH.00005: Heavy flavor tagged jet evolution in QGP using the JETSCAPE framework Wenkai Fan The dynamics of shower development for a jet traveling through the quark-gluon plasma (QGP) involves a variety of scales, including the mass for heavy flavors in jets. Though the mass of the heavy quarks plays a subdominant role during the high virtuality portion of the jet, it does affect longitudinal drag and diffusion, stimulating additional radiation from heavy quarks. These emissions partially compensate the reduction in radiation from the dead cone effect. In the lower virtuality part of the shower, when the mass is comparable to the transverse momentum of the parton, scattering and radiation processes off heavy quarks are different than off light quarks. All these factors result in a different shower development for heavy-flavor tagged jets. We present a multi-stage calculation that explores the importance of differences between various heavy quark energy-loss mechanisms. The high virtuality and low virtuality stages of quarks and gluons are simulated by the MATTER and LBT model, respectively. Those partons evolve in a realistically expanding medium, modeled on an event-by-event basis using the JETSCAPE Framework. |
Thursday, October 14, 2021 12:30PM - 12:42PM |
QH.00006: Continuous Evolution of Electromagnetic Field in Heavy-Ion Collisions Evan M Stewart, Kirill Tuchin In heavy-ion collisions the electromagnetic field exists before the hot nuclear matter emergence. Requiring the field continuity we compute it in the central rapidity region by taking into account the electromagnetic response of the Quark Gluon Plasma. I will discuss the significance of these results have on the phonomenology of heavy-ion collisions. |
Thursday, October 14, 2021 12:42PM - 12:54PM |
QH.00007: Optimization of STAR sTGC track finding using boosted decision trees Youqi Song The Forward Tracking System (FTS) is part of the STAR forward detector upgrade that will start data taking for the first time in November 2021. The FTS covers 2.5 < η < 4.0 in pseudorapidity and consists of silicon microstrip sensors and small-Strip Thin Gap Chambers (sTGC). Charged particles that originate from collisions are detected via hits in the tracking detectors. These hits are fed into an algorithm, which ends up reconstructing charged tracks. We utilize a boosted decision tree (BDT) algorithm via AdaBoost as implemented in a Scikit-learn python package to improve the sTGC tracking efficiency and purity as compared to standard cut-based approaches. We generate PYTHIA8 pp Drell-Yan events at √s = 510 GeV and construct hit pair and triplet observables from the hit locations created in the GEANT simulations of charged particles within our detector acceptance. A sequence of BDTs is then trained to evaluate tracks as real or fake, based on their hit pair and triplet observables. The trained model is then tested on PYTHIA8 Drell-Yan and soft QCD events. For both cases, the track finding performance is improved if the appropriate BDT setup is used. In this talk, I will present the BDT method that we use for STAR sTGC track finding for PYTHIA events and compare its performance with the cut-based method. |
Thursday, October 14, 2021 12:54PM - 1:06PM |
QH.00008: Calorimeteter Design and Calibration for New Experiments at RHIC and the EIC Justin Frantz, Justin Bryan New calorimeters are being both proposed and built at RHIC and for the future EIC. We will review this situation including possible and realized designs and especially focus on techniques for calibrating the new calorimeters. |
Thursday, October 14, 2021 1:06PM - 1:18PM |
QH.00009: Exploiting common-mode signals in the ALICE TPC to search for magnetic Monopoles Mesut Arslandok The magnetic monopole is a hypothetical elementary particle, beyond the Standard Model, with only one magnetic pole. It was first introduced by Paul Dirac in order to explain the quantization of electric charge. Predictions within Grand Unified Theories suggest that they are far too massive to be produced in any foreseeable accelerator. However, there are models where monopoles could appear in a mass range accessible to the LHC, with ionization equivalent ≈ 4700 minimum-ionizing particles (MIPs). The Time Projection Chamber (TPC) is the main tracking and particle identification detector of ALICE. In order to cope with the increased interaction rates of up to 50 kHz in PbPb collisions expected beyond 2020, the previously employed gated multi-wire proportional chambers have been replaced by GEM-based (Gas Electron Multiplier) readout chambers which allow for continuous readout. Due to capacitive coupling of the GEM system to the readout pads, discharging and charging of the GEM electrode induces a correlated common-mode signal with opposite polarity on all anode pads facing the GEM system in which the original signal is detected. Monopoles are expected to induce very large common-mode signals. In this contribution, a method that exploits these signals to potentially detect magnetic monopoles will be discussed. |
Thursday, October 14, 2021 1:18PM - 1:30PM |
QH.00010: Photon Radiation in Fermi-Energy Heavy-Ion Collisions Thomas J Onyango, Ralf F Rapp Electromagnetic radiation (photons and dileptons) has a long history as penetrating probes of the strongly interacting matter created in heavy-ion collisions, as it does not suffer significant final-state interactions. At ultra-relativistic collision energies, the fireball is believed to reach local equilibrium facilitating the use of well-defined thermal emission rates which can illuminate properties of the produced QCD matter (such as its temperature, lifetime, and spectral properties). The situation is less clear at lower collisions energies. Here we utilize the concept of coarse-graining of the fireball formed in nuclear collisions at Fermi energies to investigate the radiation of photons in these reactions. Utilizing results of microscopic transport simulations for nucleon positions and momenta within the Constrained Molecular Dynamics (CoMD) model, we extract the time dependence of local temperatures and chemical potentials. For the longitudinal direction, off-equilibrium effects due to the primordial motion of the incoming nuclei are essential to be accounted for. The coarse-graining results are then used to compute the emission spectra of photons employing rates for nucleon-nucleon Bremsstrahlung. The results are compared to experimental data for photon energy spectra. |
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