Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session ML: Hard Probes in High Energy Heavy Ion Collisions |
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Chair: Cesar Luiz da Silva, LANL Room: Hilton Queen's 5 |
Saturday, October 27, 2018 2:00PM - 2:15PM |
ML.00001: Open heavy-flavor production in Pb-Pb collisions measured with ALICE at the LHC Erin Gauger Heavy-flavor quarks (charm and beauty) are created in the first moments of a heavy-ion collision via hard partonic scattering processes. Therefore, they experience the full evolution of the collision and interact with constituents of the hot and dense QCD medium produced, the Quark-Gluon-Plasma (QGP), a state of matter in which quarks and gluons are deconfined. We can gain insight into the microscopic processes responsible for heavy-quark energy loss in the QGP by measuring heavy-flavor hadrons and their decay products. |
Saturday, October 27, 2018 2:15PM - 2:30PM |
ML.00002: Open heavy flavor measurements with the Forward Silicon Vertex Detector at PHENIX Xuan Li Heavy flavor production is an important hard probe to test Quantum Chromodynamics (QCD) and measure the properties of the Quark Gluon Plasma (QGP) created in high energy heavy ion collisions. Heavy flavor production at RHIC has different kinematics and different production mechanisms compared with the LHC. The PHENIX experiment has collected large data sets of 200 GeV and 510 GeV $p$+$p$ as well as a wide variety of small and large collisions systems at 200 GeV. These data sets allow us to study the energy dependence of the heavy flavor production and heavy quark energy loss in both cold and hot nuclear matter. In this talk, we will present latest PHENIX open heavy flavor results using the Forward Silicon Vertex Detector (FVTX) through the B to $J/\psi$ channel to understand the energy dependent bottom production in $p$+$p$ collisions and nuclear modification of bottom quarks in Cu+Au collisions. We will also present the analysis progress and the prospects for ongoing PHENIX forward rapidity open heavy flavor measurements in 200 GeV p+p and Au+Au collisions. |
Saturday, October 27, 2018 2:30PM - 2:45PM |
ML.00003: Measurement of electrons from heavy-flavour hadron decays in pp collisions at &[root]s = 13 TeV with ALICE Toma Suzuki Due to their large mass, heavy-flavour (charm and beauty) quarks are mostly produced in initial hard scattering processes on a shorter time scale than the formation time of the hot and dense colour-deconfined QCD matter, the so called Quark-Gluon-Plasma (QGP). When heavy quarks go through the QGP medium, they lose energy by radiative and collisional processes. Therefore, they are an effective probe to investigate the properties of the QGP. In this presentation, the measurement of the yield of electrons from heavy-flavour hadron decays in pp collisions at √s = 13 TeV performed by ALICE Collaboration will be shown. The yield has been measured up to 12 GeV/c. The high pT region (pT >12 GeV/c) will be accessible in the future by using EMCal detector and analyzing the full pp 13 TeV statistic. Thus the electrons can be measured with EMCal trigger up to higher pT region at mid-rapidity(| η |<0.6) by analyzing this data. The Inner Tracking System(ITS) and Time Projection Chamber(TPC), ElectroMagnetic Calorimeter(EMCal) detectors are used for the electron identification. The yield is obtained after subtracting the main background, hadron contaminations and photonic electrons, from the yield of the inclusive electrons. The results will be compared with a FONLL QCD prediction. |
Saturday, October 27, 2018 2:45PM - 3:00PM |
ML.00004: High-pT electrons from heavy-flavour hadron decays in p-Pb collisions at &[root]sNN = 8.16 TeV with ALICE Daichi Kawana Lattice Quantum Chromodynamics (QCD) calculation predicts that a colour-deconfined QCD matter, Quark-Gluon Plasma (QGP), is formed at high temperature and energy density reached in ultra-relativistic heavy-ion collisions. Heavy quarks (charm and beauty) are mostly produced by initial hard scatterings before the formation of the QGP. Therefore heavy-flavour hadrons are ideal probes to investigate the properties of the hot and dense QCD matter. In Pb-Pb collisions, a strong suppression of the production of heavy-flavour hadrons with high transverse momentum has been observed. |
Saturday, October 27, 2018 3:00PM - 3:15PM |
ML.00005: Isolated photon + hadron and jet correlation in pPb and pp collisions measured by ALICE Miguel I Arratia The photon-tagged correlation of jets and jet fragments is a promising channel for the study of parton energy loss in nuclear collisions. While existing measurements in pp and nuclear collisions have used high energy photons and jets, we focus on an unexplored kinematic range given by 10<pT<20 GeV/c photons and the corresponding low jet pT. We present results obtained using 5.02 TeV pp and pPb collisions. A combination of isolation and electromagnetic shower-shape variables is used to reduce the large background from meson decays and fragmentation photons. We show how the access to this kinematic range of hard probes was achieved with a novel combination of high rate and low-momentum tracking using the electromagnetic calorimeters and the Inner Tracking System of the ALICE experiment. |
Saturday, October 27, 2018 3:15PM - 3:30PM |
ML.00006: Measurement of neutral mesons in pp and Pb--Pb at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE Daiki Sekihata Neutral mesons such as $\pi^{0}$ and $\eta$ that decay into two photons can be reconstructed and identified in a wide transverse momentum ($p_{\rm T}$) range. |
Saturday, October 27, 2018 3:30PM - 3:45PM |
ML.00007: Bayesian Study of Jet Background Subtraction in Relativistic Heavy-Ion Collisions Ron Ariel Soltz, Aaron Angerami, Jason Bernstein Jets are an essential probe to study the microscopic properties of the quark gluon plasma created in relativistic heavy ion collisions, however studies of jet observables can depend upon background subtraction methods and inputs. In order to study these effects we have developed a simple model by embedding scaled pythia jets into a thermal blast-wave generated background distribution with event multiplicities and eccentricities generated by the TRENTO model. We apply a background subtraction method developed by ATLAS to jets identified using the FASTJET package, and we investigate the sensitivity to jet-finding and background subtraction using a kernel density estimator in a Bayesian approach to search for biases in the determination of the pythia scaling factor. Results are reported for several different event centrality ranges and background subtraction inputs. |
Saturday, October 27, 2018 3:45PM - 4:00PM |
ML.00008: High-pT π0-Triggered Two-Particle Azimuthal Correlations in &[root]sNN = 200 GeV d+Au Collisions at PHENIX Nathan C Grau Two-particle correlations azimuthal correlations using pairs of high-pT particles are sensitive to similar physics as fully reconstructed jets but probe a lower Q2 of the partonic interaction. Therefore, such correlations are important measurements to elucidate the physics behind multiple scatterings, energy loss, and saturation effects in d(p)+Au collisions. In particular the pseudorapidity- and pT- dependence of the away-side width of two-particle correlations is directly sensitive to the value of the color glass condensate saturation scale. In this contribution, we discuss the current status of two-particle correlations with identified π0 triggers over different pseudorapidity ranges from pairs at midrapidity to pairs at forward rapidity η~3 in 200 GeV d+Au collisions at PHENIX. <div aju"=""> |
Saturday, October 27, 2018 4:00PM - 4:15PM |
ML.00009: Multiplicity-dependent di-hadron correlations with identified leading hadrons in &[root]sNN=200 GeV d+Au collisions at STAR Kazuya Nakagawa
A growing body of evidence suggests the creation of a hot and dense partonic state of matter called Quark Gluon Plasma (QGP) in high-energy nuclear collisions even in small systems. Enormous progress has been made in recent years in the theoretical description of the QGP evolution, but one of the remaining challenges is the role of hadronization mechanisms in measured observables. Di-hadron correlations is considered a particularly valuable tool to gain further insights into recombination process that happens in the QGP. Previously, the STAR Collaboration has measured angular correlations of intermediate-pT particles with identified leading hadrons. It was found that charged-hadron jet-like yield associated with pion triggers is enhanced at intermediate-pT in Au+Au collisions compared to d+Au collisions where only minimum bias events were studied. In this talk, we will present di-hadron correlations with identified leading hadrons in d+Au collisions at √sNN=200 GeV as a function of centrality using the large data set collected in 2016. |
Saturday, October 27, 2018 4:15PM - 4:30PM |
ML.00010: Study of azimuthal anisotropy of charged hadrons at high pT in Au+Au collisions at &[root]sNN = 200GeV at RHIC-PHENIX Risa Nishitani The azimuthal anisotropy coefficient v2 is a good tool to investigate properties of the Quark Gluon Plasma (QGP). It can study not only the collective behavior of the medium, but also the energy loss of hard scattered partons in it. The non-central collisions yield the collision areas with elliptic shape. When the hard scattered partons created in the collisions are emitted, they have different path-lengths of interacting with QGP depending on their emission angles with respect to the reaction plane. This will result in the difference of the yields of high transverse momentum (pT) particles in in-plane and out-of-plane. Therefore, the energy loss mechanism can be investigated by measuring the v2 at high pT. We have recently improved the precision of the charge hadron v2 measurement by reducing background tracks using the silicon vertex tracker installed in PHENIX. In this presentation, we discuss the collision centrality dependence and pT dependence of charged hadron v2 in Au+Au collisions at √sNN=200GeV from the data collected by PHENIX during the RHIC Year-2014 run. We also discuss the path-length dependence of the energy loss utilizing the v2 measurement. |
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