Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session KG: Mini-Symposium on Jets and High pT Physics |
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Chair: Agnes Mocsy, Pratt Institute Room: Pearl Ballroom II |
Friday, October 25, 2013 2:00PM - 2:36PM |
KG.00001: Using Jets and Other High pT Probes to Understand Properties of the QGP Invited Speaker: Megan Connors In high energy collisions of heavy ions, high momentum partons traverse and lose energy in the dense medium created, known as Quark Gluon Plasma (QGP). By studying how these high momentum probes interact and lose energy in the medium we can learn more about the properties of the QGP. These partons, produced by hard scatterings early in the collision, eventually fragment into particles which can be observed by experiments and used to measure medium-induced parton energy loss. To access these probes and the medium modification of jet fragmentation, several observables have been measured from spectra and angular correlations of high momentum fragments to full jet reconstruction. By comparing these measurements in heavy ion collisions to those in pp, we can quantify the modification due to the medium and with the aid of models, begin to build a picture of the QGP and its properties. Results from a variety of collision species and energies, from the LHC and RHIC experiments, including the latest results from this year's pPb run at the LHC, and the resulting picture of the QGP will be presented. [Preview Abstract] |
Friday, October 25, 2013 2:36PM - 2:48PM |
KG.00002: Measurement of Nuclear Modifications of Jets in pPb collisions at $\sqrt{s} = 5.02$ TeV with ALICE at the LHC Chris Yaldo In heavy-ion collisions it is important to distinguish between initial and final state effects, and to estimate cold nuclear matter effects (CNM) on jet production. A crucial reference is the jet nuclear modification factor (RpPb) in pPb collisions at $\sqrt{s} = 5.02$ TeV at the LHC. Jets in ALICE are reconstructed combining information from the Time Projection Chamber (TPC), Inner Tracking System (ITS), and the Electromagnetic Calorimeter (EMCal) to measure the charged and neutral jet constituents. Measurements of the inclusive differential cross section in pPb collisions and the jet $R$pPb will be presented. The ratios of jet cross-sections for various radii, which is sensitive to the jet shape, will be discussed and compared to pp and pQCD calculations. [Preview Abstract] |
Friday, October 25, 2013 2:48PM - 3:00PM |
KG.00003: Long-range pseudo-rapidity correlations in 200 GeV Au$+$Au collisions with STAR Martin Codrington Two interesting correlation analyses that may be useful in describing the matter created in heavy-ion collisions are $\gamma $-hadron correlations and di-hadron long-range pseudorapidity correlations (the ``ridge''). $\gamma $-hadron correlations are interesting because photons do not strongly interact with partonic matter: They provide a momentum tag for the recoil hadron(s) which may provide a better understanding of the matter produced. Additional measurements of the ridge using $\pi^{0}$s at high p$_{T}$ may lead to a better understanding of ridge formation. Previously published STAR data has shown 2-D charged di-hadron correlations, and 1-D $\pi^{0}$ triggered correlations. Wewill show results of 2-D correlations of likely $\gamma $ {\&} $\pi^{0}$ triggers with charged hadrons from Au$+$Au collisions taken during Runs 7, 10, {\&} 11 with the STAR detector; using the Time Projection Chamber (TPC) and the Barrel ElectroMagnetic Calorimeter (BEMC). The TPC is used to measure the trajectory and momentum of charged hadrons and the BEMC is used to calculate the energy of electromagnetic particles. $\pi^{0}$s were reconstructed from their decay photons in the Barrel Shower-Maximum Detector which sits $\sim$ 5.6 X$_{0}$ in the BEMC. The combination of the 3 datasets should provide adequate statistics to examine the ridge at high pt above 10 GeV. [Preview Abstract] |
Friday, October 25, 2013 3:00PM - 3:12PM |
KG.00004: Direct photon-Hadron Correlations in Au+Au collisions at $\sqrt{s}=200$ GeV Measured with PHENIX Huijun Ge High momentum direct photons are produced back-to-back with partons in the initial hard scatterings in heavy ion collisions. Since such photons do not interact strongly with the quark-gluon plasma created in these collisions, their measured momentum will approximately balance that of the opposing parton prior to any medium modification. Therefore, using high-momentum direct photons as triggers and comparing the away-side yields in direct photon-hadron correlations in Au+Au collisions to those in p+p can potentially shed light on how the opposing jet is modified by the medium. This allows us to gain more insight into the parton energy loss mechanisms. We present the current status of direct photon-hadron correlation measurements in Au+Au collisions at $\sqrt{s}=200$ GeV and discuss the potential for extending such measurements with the inclusion of data taken in 2011 using the PHENIX detector at RHIC. [Preview Abstract] |
Friday, October 25, 2013 3:12PM - 3:24PM |
KG.00005: Hadron+jet coincidence measurements with ALICE Rongrong Ma The primary goal of the heavy-ion field is to study the properties of the quark-gluon plasma (QGP) created in relativistic heavy ion collisions. At the early stage of the collisions, hard scatterings of quarks and gluons (partons) take place and the scattered partons subsequently interact with the medium. The kinematics of the partons could be recovered approximately using reconstructed jets, which provides an opportunity to study the properties of the medium. One challenge for jet reconstruction in heavy-ion collisions is the large background. The hadron+jet coincidence measurement presented in this talk is designed to overcome this issue. Charged particles are used as triggers, and the charged jets recoiling back-to-back from these triggers are collected. Triggering on the charged hadrons should bias the initial hard scatterings towards the surface of the medium, such that the recoiling jets would go through longer than average length in the medium. Since the background contribution to the recoil jet spectrum is uncorrelated with the trigger hadrons, it can be removed by taking the difference of the jet spectra in different trigger intervals. Results from Pb-Pb collisions are compared to quenched models, and a baseline perturbative QCD calculation at Next-To-Leading order. [Preview Abstract] |
Friday, October 25, 2013 3:24PM - 3:36PM |
KG.00006: Comparison of AMPT and HIJING generated $p_T$ spectra at mid-rapidity to those measured in the Beam Energy Scan from STAR Stephen Horvat Quenching of high transverse momentum ($p_{T}$ ) charged hadrons can be measured by the nuclear modification factor, which compares binary collision-scaled $p_{T}$ spectra from central heavy-ion collisions to a reference spectrum, either proton-proton ($R_{AA}$) or peripheral heavy-ion collisions ($R_{CP}$) by taking their ratio. At large $\sqrt{s_{_{NN}}}$ the nuclear modification factor at high $p_{T}$ is observed to be suppressed, i.e. less than unity. The complex array of processes that can modify particle spectra in nuclear collisions span cold nuclear matter effects, a strongly-interacting medium, and an extended phase of hadronic re-scatterings. Measurements of charged hadron $R_{CP}$($\sqrt{s_{_{NN}}}$, $p_{T}$) for $\sqrt{s_{_{NN}}}$ = 7.7 - 200GeV show a smooth transition from strong enhancement of high $p_{\mathrm{T}}$ charged hadrons at low energies to strong suppression at high energies, crossing unity between 39 and 27 GeV. These data will be compared with event generators such as HIJING and AMPT. RHIC's broad range of collision systems and energies provides us with the tools to test the assumptions of the event generators; facilitating the investigation of the relative contributions from jet quenching and the Cronin Effect to spectra from heavy-ion collisions. [Preview Abstract] |
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