Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session 2WH: Workshop on the Expanding Future of High Energy Nuclear Physics at LHC and RHIC II |
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Chair: Kenta Shigaki, Hiroshima University Room: Kings 3 |
Tuesday, October 13, 2009 2:00PM - 2:30PM |
2WH.00001: Photon and Dilepton Emission from the QGP at RHIC Invited Speaker: We present a review of the theory and of the interpretation of photon and dilepton data measured in relativistic nuclear collisions at RHIC. This includes photon and lepton pair spectra from a variety of emitted sources, a discussion of the photon nuclear modification factor, and photon-jet correlations. We show that a consistent treatment of photon emission must also include a theory of jet energy loss in the strongly interacting medium. [Preview Abstract] |
Tuesday, October 13, 2009 2:30PM - 3:00PM |
2WH.00002: Measurements of low mass di-electrons and low $p_{T}$ direct photons in the PHENIX experiment at RHIC Invited Speaker: The PHENIX experiment at RHIC is suitable for measuring transparent probes such as electrons and photons, and they are powerful probes to investigate properties of the matter created in heavy ion collisions. Especially, the di-electron measurements provide us deep insight into the created matter. Recently, the low mass di-electron yield has been successfully measured in both p+p and Au+Au collisions. While the p+p result is well-understood as a combination of electron pairs from know hadronic sources, an enhancement of di-electron yield over the known hadronic sources is observed in Au+Au collisions in the low $p_{T}$ region. The various efforts for developing models have been done in order to understand the enhancement of di-electron yield in low mass and low $p_{T}$ region. But these models do not explain this enhancement fully yet. Furthermore, the fraction of the contribution from virtual direct photon decay can be determined from dielectron yield by focusing on the region which satisfies $p_{T}^{2} \gg m_{ee}^{2}$. The real direct photon yield in $p_{T}$ of 1-5~GeV/c has been obtained from the fraction of the virtual direct photon in p+p and Au+Au collisions. A significant excess over the binary scaled p+p result is seen in Au+Au collisions in this $p_{T}$ region, where the primary contributor is considered to be thermal photons from QGP. Theoretical models which can reproduce our Au+Au result indicate that the initial temperature of the created matter is higher than the critical temperature of QGP (200~MeV). In this talk, the latest results on the di-electron and virtual direct photon measurements in p+p, p+A and A+A collisions at PHENIX will be presented. [Preview Abstract] |
Tuesday, October 13, 2009 3:00PM - 3:30PM |
2WH.00003: Photon Physics Potential at ALICE Invited Speaker: The ALICE detector has been designed to study the strongly interacting matter created in nucleus-nucleus collisions at the Large Hadron Collider~(LHC). In heavy-ion collisions, it is very critical to measure thermal photons, which are known to carry the temperature information of hot created matter. The thermal photon measurements at RHIC are suggesting the systematic study with better photon detectors at LHC. Furthermore, the suppression of high $p_T$ hadrons has provided the first strong signature of hot and dense partonic matter created in heavy-ion collisions at RHIC. Therefore, the suppression behavior of various particle species, including photons, up to LHC energy, is a key observable for the study of the hot matter dynamics. The ALICE PHOton Spectrometer~(PHOS) consists of 17920 PWO crystals and Avalanche Photo Diode~(APD) covering a rapidity range of $\pm0.3$ and an azimuthal range of $100^{\circ}$. The fine segment structure and small Moliere radius allow to separate two photons from $\pi^{0}$ decay at pT=30GeV/c with about 100\% efficiency and at even higher pT with smaller efficiency. The decay photons from lower pT $\pi^{0}$ is the largest background in measuring the thermal photons and can be tagged in a very efficient way with a good energy resolution ($3\%/\sqrt{E(GeV)}$). The ALICE EMCAL consists of shashlik lead-scintillator sampling units covering a rapidity range of $\pm0.7$ and an azimuthal range of $110^ {\circ}$ and sits in the opposite coverage azimuthally to PHOS. The jet measurements by EMCAL and other tracking detectors, especially when tagged by a direct photon in the opposite PHOS detector, represent a key probe for investigating jet quenching effects. In this presentation, physics potential with photon detectors at ALICE during the first physics run of LHC will be discussed. The construction and installation status of the photon detectors as well as their expected physics will be presented. [Preview Abstract] |
Tuesday, October 13, 2009 3:30PM - 4:00PM |
2WH.00004: COFFEE BREAK
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Tuesday, October 13, 2009 4:00PM - 4:30PM |
2WH.00005: Test of Ideal Hydrodynamical Limit at RHIC Invited Speaker: Elliptic flow ($v_2$) is one of the most prominent observables to study collective properties of the hot and dense medium created in relativistic heavy ion collisions. It has been found that the ratio of $v_2$ to the initial spatial anisotropy $\varepsilon$ scales as transverse number density $1/S dN/dy$ for different collision energies and systems from AGS ($\sqrt{s_{_{NN}}} \sim$ 5 GeV) to RHIC ($\sqrt{s_{_{NN}}}$ = 200 GeV). Eventually, the linear dependence of $v_2/\varepsilon$ vs. $1/S dN/dy$ is expected to be saturated when the system reaches local thermal equilibrium. However, till now there is no sign of saturation of $v_2/\varepsilon$ at top RHIC energy. It is natural to ask the question to what extent the system has reached the ideal hydrodynamical limit. It is also important to understand how the $v_2/\varepsilon$ behaves at higher transverse number density. Compared to Au nucleus, uranium is a heavier and naturally deformed. The planned U~+~U collisions at RHIC (2012) could provide higher densities than that achieved in Au~+~Au collisions. In this talk, we present the results of a test on ideal hydrodynamical limit. The $v_2$ data from Au~+~Au collisions at $\sqrt{s_{_{NN}}}$~=~200~GeV are used. It has been found that even at most central Au~+~Au collisions the ideal hydrodynamical limit has not been reached. In addition, we present the prediction of $v_2$ in U~+~U collisions at $\sqrt{s_{_{NN}}}$~=~200~GeV by extrapolating the measured $v_2$ in Au~+~Au collisions at RHIC. [Preview Abstract] |
Tuesday, October 13, 2009 4:30PM - 5:00PM |
2WH.00006: The Long Slow Death of the HBT Puzzle Invited Speaker: Over the past 20 years two particle-correlations between identical pions have developed into a quantitative tool to test the space-time evolution of heavy-ion collisions. Surprisingly, correlations from RHIC failed to match expectations from hydrodynamic-based models, as the model-predicted source sizes were sometimes 50\% higher than was inferred from experiment. This failure became known as the HBT puzzle (Hanbury-Brown and Twiss were pioneers in the original technique). Since the success of these very models in predicting spectra and elliptic flow was central to the discovery of the ``perfect fluid,'' the failure of their HBT predictions was disquieting. In this talk, I will show how the discrepancy can be explained by the conspiracy of three effects: pre-equilibrium flow, using a stiffer equation of state and adding a modest viscosity. I will review the progress in finding a single description that reproduces the totality of soft bulk observables at RHIC. [Preview Abstract] |
Tuesday, October 13, 2009 5:00PM - 5:30PM |
2WH.00007: The ALICE experiment -- Nuclear collisons at the high-energy frontier at LHC Invited Speaker: A Large Ion Collider Experiment (ALICE) is the dedicated experiment for studying nuclear collisions at the LHC. It will address the physics of QCD matter under extreme conditions of temperature and energy density. ALICE is an international collaboration of more than 1000 physicists and engineers from presently 105 institutions. First p+p collisions provided by LHC are expected at the end of this year. The current status of the ALICE experiment, its instrumentation and performance capabilities are presented. The ALICE physics potential is highlighted by discussing some selected examples scheduled for first p+p collisions, and subsequent Pb+Pb collisions. [Preview Abstract] |
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