Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session P7: Mini-Symposium: Electromagnetic Radiation from Quark-Gluon Plasma |
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Sponsoring Units: DNP Chair: Charles Gale, McGill University Room: Delaware A |
Monday, February 15, 2010 10:45AM - 11:21AM |
P7.00001: Enhanced production of direct photons in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV and implications for the initial temperature Invited Speaker: The production of $e^+e^-$ pairs for $m_{e^+e^-}<300$ MeV/$c^2$
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Monday, February 15, 2010 11:21AM - 11:33AM |
P7.00002: Feasibility study of the two-photon intensity interferometry in Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV from PHENIX at RHIC Xiaoyang Gong, Roy Lacey, Jiangyong Jia, Rui Wei Two-particle intensity interferometry is an important probe for the dynamical evolution of the quark-gluon plasma produced in heavy ion collisions at RHIC. Recent RHIC measurements have predominantly focused on two-pion intensity interferometry studies. However, two-photon measurements can provide significant additional insights, since photons are emitted throughout the whole dynamical evolution of the fireball and from every point in the system -- not only from the freeze-out surface. Moreover, photons interact only weakly with the system after their production and are free from the distorting effects of re-scattering and Coulomb interactions. Two-photon interferometry measurements continue to be a significant challenge due to the large background of decay photons and a relatively small production rate of direct photons at low $p_T$. In recent experiments, the PHENIX collaboration has embarked on a program aimed at extensive two-photon interferometry measurements in Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV. The latest results from these measurements will be presented and their implications for reaction dynamics and the yield of direct photons will be discussed. [Preview Abstract] |
Monday, February 15, 2010 11:33AM - 11:45AM |
P7.00003: Medium and high $p_T$ direct photons in PHENIX Gabor David We will present a critical survey of published and recent preliminary results on direct photon production observed by PHENIX in various colliding systems and energies. Within current systematic errors all available p+p data are consistent with NLO pQCD calculations and after proper scaling and accounting for the isospin effect the heavy ion data are also consistent with the dominance (exclusivity?) of primordial hard scattering. In other words, no evidence of additional production (like jet-photon conversion) or change of nPDFs has been found so far, nor has a clean signal of direct photon flow been seen. However, all these effects are predicted to be relatively small and may just be obscured by earlier experimental uncertainties. In light of the latest available high statistics data we will review what (if any) new conclusions can be drawn on various mechanisms of direct photon production at medium and high $p_T$ in heavy ion collisions. [Preview Abstract] |
Monday, February 15, 2010 11:45AM - 11:57AM |
P7.00004: High $p_T$ hadron production and its quantitative constraint to model parameters at PHENIX Takao Sakaguchi Hot and dense matter created in relativistic heavy ion collisions is found to be opaque according to the fact that the yield of high $p_T$ hadrons, which are considered to carry the major fraction of the momentum of hard scattered partons, is highly suppressed. The nuclear modification factors ($R_{AA}$) of $\pi^0$ from the latest PHENIX publication [Phys.Rev.Lett. {\bf 101}, 232301(2008)] are found to be consistent with linear increase as a function of $p_T$. These developments have stimulated the development of several theoretical models. By properly accounting for the statistical and various types of experimental, but not theoretical, systematic errors, the PHENIX experiment has recently succeeded in obtaining quantitative constraints on energy loss within the context of each model. There is a limitation on detecting high $p_T$ $\pi^0$ because of merging $\gamma$'s decaying from $\pi^0$, but we found that we can reach four times higher $p_T$ when looking at $\eta$. We analyzed data from the RHIC Year-7 Au+Au run and obtained $\eta$ $p_T$ spectra and $R_{AA}$ up to 21\,GeV/c with a smaller systematic error compared to that of $\pi^0$. The result shows the similar trend in suppression as $\pi^0$. In this presentation, an attempt to constrain model parameters using the latest high $p_T$ $\eta$ spectra from PHENIX will be shown, and the characteristics of the matter produced obtained in the study will be discussed. [Preview Abstract] |
Monday, February 15, 2010 11:57AM - 12:09PM |
P7.00005: Measurement of Low Transverse Momentum Direct Photons Via External Conversions in Au+Au Collisions at $\sqrt{s} = 200$ GeV with the PHENIX Detector at RHIC Richard Petti Photons are an important probe of the hot and dense partonic medium created through the collision of heavy ions at the Relativistic Heavy Ion Collider (RHIC), located at Brookhaven National Laboratory. This is because they escape the medium with no modification and carry information about the earliest stages of the collision. This analysis measures low transverse momentum direct photons in Au+Au collisions at $\sqrt{s} = 200$ GeV as seen in the central arms of PHENIX ($|\eta|<0.35$) during the 2007 data taking period. These measurements can then be compared to theoretical expectations. An inclusive real photon spectrum is obtained by measuring dilepton pairs that have been identified as photons converting in detector material. These dilepton pairs from real photons can be identified by cutting on the orientation of the opening plane of the pair relative to the magnetic field in the detector. A neutral pion tagged sample is also measured and other expected hadronic contributions are simulated based on actual measurements. An excess of direct photons above the inclusive sample are then quantified as a ratio of inclusive to hadronic decay photons. The status of this analysis will be discussed. [Preview Abstract] |
Monday, February 15, 2010 12:09PM - 12:21PM |
P7.00006: Direct Photon-Hadron Correlations Measured in Au+Au Collisions at $\sqrt{s_{NN}}=200$ with the PHENIX Detector Megan Connors Direct photon-hadron correlations are an excellent channel for studying jet tomography of the medium produced in heavy ion collisions at RHIC. Since photons do not interact strongly with the medium, the photon approximately balances the momentum of the opposing jet. Determining the initial momentum of the jet allows for measurement of the effective modification to the fragmentation function through jet energy loss in the medium by comparing the away-side yield of the correlations in Au+Au to those in p+p. However, this measurement is complicated by the need to remove the contribution of photons from jet fragmentation processes from the inclusive photon correlations. PHENIX has established the ability to extract the direct photon-hadron correlations via a statistical subtraction procedure. To improve the uncertainties in the measurement, event by event techniques have also been studied. The latest PHENIX measurements along with comparisons to theoretical models will be presented. [Preview Abstract] |
Monday, February 15, 2010 12:21PM - 12:33PM |
P7.00007: A New Method for Detecting a Possible Parity Violating Signal in Heavy Ion Reactions at RHIC N.N. Ajitanand Theoretical studies have suggested that the new phase of nuclear matter that is created in heavy-ion collisions is a good testing ground for possible violation of space and time reflection symmetry [1,2]. Recent attention has centered on the possibility that signatures for parity violation may be produced by the topological charge generated early in the process leading to QGP formation in RHIC collisions [1,2]. The strong magnetic fields developed along the orbital angular momentum (L) axis is expected to cause movement of these charges resulting in a small charge asymmetry in the angular distribution of hadrons in an event. A novel analysis method has been developed which has the required sensitivity to detect small but specific shape differences in the azimuthal angular distribution of positive and negative charges with respect to the reaction plane. Results from model simulations will be used to demonstrate the efficacy of the method, and results from application of the method to PHENIX Run-7 Au+Au data will be presented. \newline \newline 1.D. Kharzeev, R. D. Pisarski, and M. H. G. Tytgat, Phys. Rev. Lett. 81, 512 (1998). 2.D. Kharzeev and R. D. Pisarski, Phys. Rev. D 61, 111901 (2000). [Preview Abstract] |
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