Thu·Sep 22, 2011Thursday·September 22, 2011

1. 01*

   Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 62 and 200 GeV

   STAR Collaboration: G. Agakishiev · M.M. Aggarwal · Z. Ahammed · A.V. Alakhverdyants · I. Alekseev · J. Alford · B.D. Anderson · C.D. Anson · D. Arkhipkin · G.S. Averichev · J. Balewski · D.R. Beavis and 343 other authors

   We present two-dimensional (2D) two-particle angular correlations on relative pseudorapidity $\eta$ and azimuth $\varphi$ for charged particles from Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=62$ and 200 GeV with transverse momentum $p_t\ge 0.15$ GeV/$c$, $|\eta |\le 1$ and $2\pi$ azimuth. Observed correlations include a {same-side} (relative azimuth $<\pi /2$) 2D peak, a closely-related away-side azimuth dipole, and an azimuth quadrupole conventionally associated with elliptic flow. The same-side 2D peak and away-side dipole are explained by semihard parton scattering and fragmentation (minijets) in proton-proton and peripheral nucleus-nucleus collisions. Those structures follow N-N binary-collision scaling in Au-Au collisions until mid-centrality where a transition to a qualitatively different centrality trend occurs within a small centrality interval. Above the transition point the number of same-side and away-side correlated pairs increases rapidly {relative to} binary-collision scaling, the $\eta$ width of the same-side 2D peak also increases rapidly ($\eta$ elongation) and the $\varphi$ width actually decreases significantly. Those centrality trends are more remarkable when contrasted with expectations of jet quenching in a dense medium. Observed centrality trends are compared to {\sc hijing} predictions and to the expected trends for semihard parton scattering and fragmentation in a thermalized opaque medium. We are unable to reconcile a semihard parton scattering and fragmentation origin for the observed correlation structure and centrality trends with heavy ion collision scenarios which invoke rapid parton thermalization. On the other hand, if the collision system is effectively opaque to few-GeV partons the observations reported here would be inconsistent with a minijet picture.

   nucl-exPRC(2012)·104 citations
2. 02*

   Inclusive Distribution of Fully Reconstructed Jets in Heavy Ion Collisions at RHIC: Status Report

   Gabriel de Barros🇧🇷

   We present an update to the analysis of fully reconstructed jets in heavy ion collisions by the STAR Collaboration at RHIC. We analyse the response of the anti-$k_T$ algorithm in the presence of background, and present a new observable for the measurement of inclusive jet production that is expected to be more robust against background model assumptions than previous jet analyses at RHIC and LHC.

   ↳ hep-exnucl-exAIP Conf.Proc.(2012)·5 citations
3. 03*

   Viscous photons in relativistic heavy ion collisions

   Maxime Dion🇨🇦 · Jean-Francois Paquet🇨🇦 · Bjoern Schenke🇺🇸 · Clint Young🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

   Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.

   ↳ hep-phnucl-exnucl-thPRC(2011)·116 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.