Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session J15: Hot, Dense Matter in High Energy Heavy Ion Collisions II |
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Sponsoring Units: DNP Chair: Bolek Wyslouch, Massachusetts Institute of Technology Room: Hyatt Regency Jacksonville Riverfront City Terrace 11 |
Sunday, April 15, 2007 10:30AM - 10:42AM |
J15.00001: System Size and Energy Dependence of Jet-Induced Hadron-Hadron Angular Correlations in Heavy Ion Collisions at PHENIX Michael McCumber The observation of jet quenching in ultra-relativistic heavy ion collisions demonstrates significant energy loss of fast partons passing through the created medium. Azimuthal angular correlations allow for further study of the medium-induced energy loss, the energy loss mechanism, and responses of the medium to the deposited energy. We present azimuthal angle correlation results for intermediate transverse momentum charged hadrons in Cu+Cu and Au+Au collisions at both $\sqrt{s_{NN}}$ = 62.4 and 200 GeV at RHIC. Focus is given to away-side jet-induced characteristics of the correlations. We find that the jet-induced away-side distribution is broadened, non-Gaussian, and peaked away from $\Delta\phi=\pi$ in central and semi-central collisions in both heavy ion systems. The away-side broadening and peak location are found to depend upon the number of participants in the collision, but do not strongly depend on the collision energy or beam nuclei. Additional studies of the transverse momentum dependence and other properties of the jet-induced correlations will be discussed. [Preview Abstract] |
Sunday, April 15, 2007 10:42AM - 10:54AM |
J15.00002: Measurement of direct photons with a new $\pi^{0}$ tagging method in $\sqrt{s}=200Gev$ AuAu Collision at PHENIX Haijiang Gong Direct photons provide a tool to study the different stages of a heavy ion collision, especially the formation of a quark-gluon plasma, without being influenced by the strong interaction and hadronization processes. The yield of direct photons can be determined based on the double-ratio $(\gamma_{inclusive}/\gamma(\pi^{0}))_{measured}/(\gamma_{decay}/\gamma(\pi^{0}))_{calculated}$ technique. A new method to determine the double-ratio is presented, which should lead to smaller systematic errors at low $p_{T}$. It uses strict photon identification in the EMCAL and a charged particle veto to extract a clean photon signal. The clean photons are then tagged with EMCAL photon candidates, which can be reconstructed with high efficiency, to determine the fraction of photons originating from $\pi^{0}$ decays. Many systematic uncertainties and detector effects cancel in this method. The status of this analysis and comparison with previous published results will be discussed. [Preview Abstract] |
Sunday, April 15, 2007 10:54AM - 11:06AM |
J15.00003: Disentangling the Away-Side jet contributions of two-particle $h^{\pm}$-$h^{\pm}$ correlations in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV Eric Vazquez A hot dense medium exceeding the critical energy density for the partonic state of matter is created in Au+Au collisions at RHIC. This dense matter is extremely opaque to high energy partons and therefore leads to strong modifications of di-jets traversing the medium. These modifications are typically studied by comparing the di-hadron azimuth correlation functions in Au+Au collisions to those in p+p collisions. A cone-like structure is observed in the away side jet at low $p_T$, which has led to various interpretions attempting to explain such modifications. We present a method for distinguishing possible contributions to the away side jet for di-hadron azimuthal correlation in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV using unidentified charged hadrons at different $p_T$ and centrality bins. [Preview Abstract] |
Sunday, April 15, 2007 11:06AM - 11:18AM |
J15.00004: Dielectron Mass Spectra from $\sqrt{s_{\rm NN}}$ = 200 GeV Cu+Cu Collisions Measured by PHENIX Sarah Campbell The dielectron mass spectra is rich in physics signals including vector meson decays, hadron Dalitz decays, correlated semi-leptonic heavy flavor decays and direct virtual photon emission. In medium mass modifications of light vector mesons due to the QCD phase transition, the effects of chiral symmetry restoration as well as thermal radiation, may be detectable in the low mass region. The PHENIX $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au analysis suggests the following centrality dependent trends: an excess in the the low mass region of the central Au+Au spectra over the expected reference cocktail of known hadronic sources, and a suppression pattern in the intermediate region, where correlated charm dominates. The status of the PHENIX $\sqrt{s_{\rm NN}}$ = 200 GeV Cu+Cu analysis, in minimum bias and separated into centrality classes, will be presented. Similar centrality dependent trends may be evident in Cu+Cu. Comparisons between the Au+Au and the Cu+Cu spectra in centrality classes may be sensitive to surface area and volume effects. [Preview Abstract] |
Sunday, April 15, 2007 11:18AM - 11:30AM |
J15.00005: Di-Hadron Azimuthal Correlations Relative to the Reaction Plane Aoqi Feng Modification of di-hadron azimuthal correlations at large transverse momenta are a powerful tool to study the properties of the QCD matter created at the Relativistic Heavy-Ion Collider. The away-side correlation is observed to be strongly suppressed at intermediate to high pt and enhanced at low pt, indicating strong interactions between high energy partons and the created bulk medium (jet quenching). It was further observed that the away-side di-hadron azimuthal correlation is less suppressed when the high pt trigger particle is oriented in the reaction plane than perpendicular to the reaction plane, qualitatively consistent with the pathlength dependence of jet quenching. In this analysis, we compare the correlations between in- and out-of-plane at low associated pt. We also study the evolution of the correlation with respect to the orientation of the trigger particle relative to the reaction plane. we report on the status of an analysis of di-hadron azimuthal correlations relative to the reaction plane with increased statistics from RHIC. These studies will provide new inputs to our understanding of the jet-quenching phenomenon and the role of the geometry. [Preview Abstract] |
Sunday, April 15, 2007 11:30AM - 11:42AM |
J15.00006: Lineshape and elliptic flow of phi-mesons in AA collisions at $\sqrt{s_{NN}}$ = 200 GeV measured by the PHENIX experiment Hugo Valle The phi meson mass centroid and width may provide information about partial chiral symmetry restoration in the hot and dense medium. The similar mass of the phi meson and the proton also makes the phi meson a good probe to study the baryon/meson anomaly in hadron production at intermediate transverse momentum (2 GeV/c $<$ p$_T$ $<$ 5 GeV/c). The PHENIX experiment has studied the lineshape, the transverse momentum spectra and the elliptic flow of phi mesons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in the phi-$>$K+ K- decay channel. An extended study using Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV is underway. The status of the analysis in the Cu+Cu system will be presented. [Preview Abstract] |
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