Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session D12: Jet Physics in Heavy Ion CollisionsLive
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Sponsoring Units: DNP Chair: Jamal Jalilian-Marian, CUNY |
Saturday, April 17, 2021 1:30PM - 1:42PM Live |
D12.00001: Determining the jet transport coefficient $\hat{q}$ of the quark-gluon plasma using Bayesian parameter estimation James Mulligan We present a new determination of $\hat{q}$, the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $\hat{q}$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These results are based on a multi-stage theoretical approach to in-medium jet evolution with the MATTER and LBT jet quenching models. The functional dependence of $\hat{q}$ on jet energy, virtuality, and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. These results provide state-of-the-art constraints on $\hat{q}$ and lay the groundwork to extract additional properties of the quark-gluon plasma from jet measurements in heavy-ion collisions. [Preview Abstract] |
Saturday, April 17, 2021 1:42PM - 1:54PM Live |
D12.00002: Measurement of the sensitivity of two particle correlations in $pp$ collisions at 13 TeV to the presence of jets with the ATLAS detector Pengqi Yin Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\Delta\eta$ that are strikingly similar to those seen in heavy-ion collisions. In heavy-ion collisions, the long-range correlations are known to arise from the collective dynamics of the produced quark-gluon plasma (QGP). The similarity between the $pp$ and heavy-ion measurements raises the possibility that a tiny droplet of the QGP is produced even in $pp$ collisions. However, models that attribute the correlation in $pp$ collisions to semi-hard processes can qualitatively reproduce the measurements. Thus performing the $pp$ measurements with an active rejection of particles associated with semi-hard processes, such as low-$p_{\mathrm{T}}$ jets, can further elucidate the origin of the long-range correlations. This talk presents measurements of two-particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV when removing tracks associated with jets from the event. It is demonstrated that such removal of particles in the vicinity of jets affects the magnitude of long-range correlations only by a few percent. [Preview Abstract] |
Saturday, April 17, 2021 1:54PM - 2:06PM Live |
D12.00003: Photon and Neutral Meson Production in pPb Collisions at LHCb Thomas Boettcher The LHCb detector provides the opportunity to study heavy ion collisions at forward rapidities at LHC energies. Photon and light neutral meson production measurements in pPb collisions at LHCb provide sensitivity to the partonic structure of the nucleus in previously unexplored kinematic regimes. An overview of measurements of photon and light neutral meson production at LHCb is presented. [Preview Abstract] |
Saturday, April 17, 2021 2:06PM - 2:18PM Live |
D12.00004: Model Studies of Measuring Fragmentation Functions Using Jet Hadron Correlations Charles Hughes, Christine Nattrass, William Witt, James Neuhaus, Adam Matyja, Soren Sorensen, Alexander Aukerman, Redmer Bertens An important observable for studying partonic energy loss in high energy nucleus-nucleus collisions is the jet fragmentation function. Detailed investigation of low momentum (10-60 GeV) jet fragmentation functions may complement previous studies by providing more information on energy loss. The main difficulty in studying low momentum jets in heavy ion collisions is the presence of a significant uncorrelated background of low momentum hadrons from soft processes. One way to deal with this background is to use the jet-hadron azimuthal correlation to fit and subtract the soft, flow correlated background information from the jet. This technique allows one to measure the near side yield in the correlation function after background subtraction for a large number of events binned in jet transverse momentum and hadron transverse momentum. From these yields binned in transverse momentum, one can then construct a fragmentation function. We discuss the specifics of this proposed method of measuring the fragmentation function including corrections for detector effects. We present the results of a Monte Carlo study using Pythia and a custom made Heavy Ion Background Generator (along with mocked up detector effects) that demonstrate the feasibility of this method. [Preview Abstract] |
Saturday, April 17, 2021 2:18PM - 2:30PM Live |
D12.00005: Jet Quenching: A Machine Learning Approach Lihan Liu Recent study has shown success in measuring the substructure of jets which cast lights on the exploration of jet quenching phenomenon. It’s believed that jets interact with the hot and dense medium, known as quark gluon plasma (QGP), which leads to both energy lost and modifications on jet substructure. Modifications on jet substructure variables reflect quenching effect. In my study, sequential variables are extracted from jet clustering history which are then used to train a Long Short-term Memory (LSTM) neural network. The LSTM neural network is a special type of Recurrent Neural Network (RNN) that learns on sequential data. Supervised machine learning strategy is performed and a well-trained neural network is able to identify quenched jets. My study has shown that jet clustering history and substructure variables imply quenching effect. It also shows the LSTM neural network is very promising in the study of jet quenching phenomenon. [Preview Abstract] |
Saturday, April 17, 2021 2:30PM - 2:42PM Live |
D12.00006: Measurement of the suppression of large-radius jets and its dependence on substructure in Pb+Pb and pp collisions with ATLAS Wenkai Zou Measurements of the jet substructure in Pb+Pb collisions provide insight into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions, over a wide range of energy scales. This talk presents the ATLAS measurement of the suppression of yields of $R=0.2$ small-radius jets and re-clustered $R=1.0$ large-radius jets. The yield suppression measurement based on the large-radius jets is performed with dependence on the jet substructure, characterized by the angular correlation and splitting scale of their sub-jets produced in the earliest splitting. This measurement utilizes the large Pb+Pb data sample at the center-of-mass energy of 5.02 TeV recorded in 2018 and is compared to the result from 2017 $pp$ collisions at the same collision energy. This study of the suppression of yields of small-$R$ jets and re-clustered large-$R$ jets brings new information about the interaction of the parton shower with the medium and tests the sensitivity of the jet quenching to the color coherence effects. [Preview Abstract] |
Saturday, April 17, 2021 2:42PM - 2:54PM Live |
D12.00007: Jet-Conversion Photons in Relativistic Heavy Ion Collisions Rouzbeh Modarresi Yazdi, Charles Gale, Sangyong Jeon Photons are powerful probes of the quark-gluon plasma (QGP). They are created at all stages of the evolution and carry information about the local conditions of their creation. As they interact only via electromagnetism, they can faithfully carry this information to the detectors. However, it is difficult to experimentally distinguish between photons of different origin. Thus it is important to have a detailed understanding of the various production mechanisms of photons in heavy ion collisions. Here we present, for the first time, a modern calculation of an important source of photons: jet-conversion photons. Using kinetic theory at leading order in the strong coupling, we calculate the rate of parton to photon conversion. The perturbative calculation is then performed using MARTINI, a Monte-Carlo algorithm for realistic jet energy loss in a strongly interacting medium. We use QGP evolution history generated using MUSIC, a realistic (3+1)D relativistic hydrodynamic simulation of a heavy ion collision. The resulting photon yields are compared to data for Au-Au at 200 GeV and Pb-Pb at 2.76 TeV. We also present our prediction of photon yield for Pb-Pb collisions at 5.02 TeV. [Preview Abstract] |
Saturday, April 17, 2021 2:54PM - 3:06PM Live |
D12.00008: Semi-inclusive hadron+jet measurement in $\rm Ru$+$\rm Ru$ and $\rm Zr$+$\rm Zr$ collisions at $\sqrt {s_{\rm NN}}=$200 GeV with the STAR experiment Yang He Jet quenching arises from jet-medium interactions in the Quark-Gluon Plasma (QGP) created in high-energy collisions of large nuclei, such as Au or Pb. The study of jet quenching in small systems, e.g. p+A collisions, has generated great interest in the community due to its relatively smaller initial energy density, temperature, and size of the created medium. Isobar collisions ($\rm Ru^{44}_{96}$+$\rm Ru^{44}_{96}$ and $\rm Zr^{40}_{96}$+$\rm Zr^{40}_{96}$) at RHIC can also be used to study jet quenching in small systems. Semi-inclusive distributions of charged-particle jets recoiling from a high transverse-momentum hadron trigger (h+jet) show a suppression in central relative to peripheral events in $\rm Au$+$\rm Au$ collisions at $\sqrt {s_{\rm NN}}=$ 200 GeV at RHIC. Utilizing the mixed-event technique to correct for uncorrelated combinatorial background present in heavy-ion collisions, we will present our preliminary measurements of uncorrected semi-inclusive h+jet for different jet radii using anti-k$_{T}$ jet reconstruction algorithm in these isobar collisions. [Preview Abstract] |
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