Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session D7: Soft and Hard Interactions at RHIC |
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Sponsoring Units: DNP Chair: Nathan Grau, Columbia University Room: Delaware A |
Saturday, February 13, 2010 1:30PM - 1:42PM |
D7.00001: Measurements of High pT $\pi^0$ Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV at PHENIX Rui Wei The phenomena of jet suppression has been well established via separate measurements of the nuclear modification factor $R_{AA}$, azimuthal anisotropy and di-hadron correlations. The current challenge is to quantitatively understand the underlying suppression mechanism, as well as to understand the interplay between jet suppression, collective flow and coalescence as function $p_T$. Meeting this challenge requires new measurements which extend the current experimental $p_T$ reach and combine the constraining power of $R_{AA}$ and anisotropy. In a recent experimental run (Year-2007), the PHENIX experiment collected over 800 $\mu b^{-1}$ in integrated luminosity of Au+Au collisions. Augmented with newly installed high resolution reaction plane detectors, this wealth of high statistics data allows detailed measurements of $R_{AA}$ relative to the reaction plane. The results using $\pi^0$s will be presented and compared with various energy loss model calculations. We will also study the $v_2$ results in different $p_T$ regions, and compare them using reaction plane determined in various $\eta$ windows. The former can shed light on the interplay between jet suppression, collective flow and coalesces, the later can help us to quantify the non-flow effects due to jets. [Preview Abstract] |
Saturday, February 13, 2010 1:42PM - 1:54PM |
D7.00002: Effects of Fluctuations in the Fireball on Jet Quenching Observables at RHIC Ricardo Rodriguez-Pedraza, Rainer Fries, Enrique Ramirez-Homs In high energy nuclear collisions, jet energy loss is usually modeled with smooth, homogeneous backgrounds. We study the effect of realistic, inhomogeneous backgrounds by implementing Glauber profiles with fluctuations. We observe how the extraction of the energy loss parameter is affected by these fluctuations and we calculate their effect on observables like single hadron spectra, nuclear modification factor, azimuthal asymmetry, back-to-back correlations and triggered fragmentation functions. [Preview Abstract] |
Saturday, February 13, 2010 1:54PM - 2:06PM |
D7.00003: Inclusive Jet and Dijet Cross Section Measurements in Polarized Proton-Proton Collisions at 200 GeV at STAR Tai Sakuma The STAR detector at the RHIC polarized proton-proton collider has full-azimuth calorimeter and tracking devices well suited for full jet reconstruction for the pseudorapidity range $|\eta| \le 1$. We report the status of the inclusive jet and dijet cross section measurements in proton collisions at 200 GeV. The jet cross sections are fundamental quantities to test the framework of the QCD factorization and perturbative QCD calculations. Dijet measurements provide additional sensitivity to parton kinematics. The jet cross sections are important steps to interpret jet spin asymmetries in polarized proton collisions that we measure to constrain the polarized gluon distribution of the proton in order to understand the spin structure of the proton. [Preview Abstract] |
Saturday, February 13, 2010 2:06PM - 2:18PM |
D7.00004: Determining sampled luminosity in proton-proton collisions at $\sqrt{s}= 500$~GeV at STAR using the vernier scan technique Ross Corliss The STAR experiment at RHIC serves as an excellent laboratory for studying spin in QCD. Comparing predicted and measured cross sections requires accurate measurements of the luminosity. At RHIC, the absolute luminosity of colliding beams is determined through a vernier scan, where trigger rates at STAR are recorded as a function of the impact parameter of RHIC's two proton beams. The details of this method as implemented at STAR will be presented. In particular, the status of the analysis of a 2009 $\sqrt{s}= 500$~GeV trigger based on the STAR barrel electromagnetic calorimeter will be shown. [Preview Abstract] |
Saturday, February 13, 2010 2:18PM - 2:30PM |
D7.00005: A new pixel sensor concept for Heavy Flavor Tracker in STAR at RHIC Xiangming Sun, Leo Greiner, Michal Szelezniak, Howard Wieman A new pixel sensor concept is proposed and simulated to improve the performance of the Heavy Flavor Tracker in STAR at RHIC. The new sensor is a multi-wire chamber with silicon readout connected. The new sensor uses the standard CMOS technology to fabricate. It inherits merits from both multi-wire chamber and silicon active pixel sensor. The new sensor can have high position resolution and high signal to noise ratio. It also has high radiation tolerance by removing the sensor diode from silicon. The new sensor also can have fast and flexible on-chip readout. [Preview Abstract] |
Saturday, February 13, 2010 2:30PM - 2:42PM |
D7.00006: Study of mutual influence of jet and flow In heavy ion collisions using AMPT model Soumya Mohapatra, Jiangyong Jia, Zi-Wei Lin, ShinIchi Esumi The two particle correlations in heavy ion collisions are often analyzed using a two source model: high energy jets that are produced during the early stages of the collision and the collective flow of the bulk medium which is a result of its (ideal) fluid like behavior and its initial geometrical anisotropy. Such analysis reveals striking features, such as suppression of away side jet and Mach-Cones. However, the two source model has the disagreeable assumption that the jet and flow are independent of each other, which casts doubts over the results obtained using this model. In order to get an understanding of jet-flow correlations and test the validity/failure of the two source model, we study simulations of Au-Au collisions at RHIC energies using the AMPT model. To isolate the effects of the jet, we simulate events with and without high $p_T$ jets and compare azimuthal distributions and $p_T$ spectrum of particles as well as the two particle correlations. We will discuss the effects of the Jet on the above mentioned observables and how the jet can both enhance and reduce the $V2$ depending on the $p_T$ of the observed particles and the embedded jet. [Preview Abstract] |
Saturday, February 13, 2010 2:42PM - 2:54PM |
D7.00007: RHIC Motivated Hydrodynamics from a Schwarzschild Black Hole James Alsup, George Siopsis We discuss the derivation of dissipative Bjorken hydrodynamics from a Schwarzschild black hole in asymptotically AdS spacetime in the limit of large longitudinal proper time $\tau$. Using an appropriate slicing near the boundary, we calculate the Schwarzschild metric to next-to-next-to-leading order in the large $\tau$ expansion as well as the dual stress-energy tensor on the boundary via holographic renormalization. At next-to-next-to-leading order, it is necessary to perturb the Schwarzschild metric in order to maintain boost invariance. The perturbation has a power law time dependence and leads to the same value of the ratio of viscosity to entropy density, $1/(4\pi)$, as in the case of sinusoidal perturbations. Our results are in agreement with known time-dependent asymptotic solutions of the Einstein equations in five dimensions. [Preview Abstract] |
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