Fri·Jul 17, 2009Friday·July 17, 2009

1. 01*

   Universal Centrality and Collision Energy Trends for $v_2$ Measurements From 2D Angular Correlations

   STAR collaboration: David Kettler🇺🇸

   We have measured the $p_t$-integrated quadrupole component of two-particle azimuth correlations (related to quantity $v_2$, denoted in this case by $v_2\{2D\}$) via two-dimensional (2D) angular autocorrelations on $(\eta ,\varphi )$ for unidentified hadrons in Au-Au collisions at 62 and 200 GeV. The 2D autocorrelation provides a method to remove non-quadrupole contributions to $v_2$ (conventionally termed ``nonflow'') under the assumption that such processes produce significant dependence on pair-wise relative $\eta$ within the detector acceptance. We hypothesize, based on empirical observations, that non-quadrupole contributions are dominated by minijets or minimum-bias jets. Using the optical Glauber eccentricity model for initial-state geometry we find simple and accurate universal energy and centrality trends for the quadrupole component. Centrality trends are determined only by the initial state (impact parameter $b$ and center-of-mass energy $\sqrt{s_{NN}}$). There is no apparent dependence on evolving system dynamics (e.g., equation of state or number of secondary collisions). Our measurements of the quadrupole and non-quadrupole components have implications for the contributions to $v_2$. They suggest that the main source of the difference between $v_2\{2\}$ and $v_2\{4\}$ (or $v_2\{2D\}$) is measured properties of minijets.

   nucl-exEPJC(2009)·52 citations
2. 02*

   Ridge, Bulk, and Medium Response: How to Kill Models and Learn Something in the Process

   J.L. Nagle🇺🇸

   In these proceedings, we highlight experimental data (published and preliminary) related to jet quenching and the response of the medium to this deposited energy. Signatures in two- and three- particle hadron correlations indicate interesting structures near the trigger particle in azimuth and over a broad range in pseudo-rapidity, often termed "the ridge", and conical-like structures separated in azimuth opposite to the trigger particle. We review numerous theoretical interpretations of the ridge in particular with a critical eye for the key properties that allow one to discriminate between, or rule out, certain physical pictures and models (and hopefully learn something in the process).

   nucl-exNPA(2009)·28 citations
3. 03*

   Neutral Pion Production in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV

   STAR Collaboration: B. I. Abelev · et al

   The results of mid-rapidity ($0<y<0.8$) neutral pion spectra over an extended transverse momentum range ($1<p_T<12$ GeV/$c$) in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions, measured by the STAR experiment, are presented. The neutral pions are reconstructed from photons measured either by the STAR Barrel Electro-Magnetic Calorimeter (BEMC) or by the Time Projection Chamber (TPC) via tracking of conversion electron-positron pairs. Our measurements are compared to previously published ${\pi }^{\pm }$ and ${\pi }^0$ results. The nuclear modification factors $R_{\mathrm{CP}}$ and $R_{\mathrm{AA}}$ of ${\pi }^0$ are also presented as a function of $p_T$ . In the most central Au+Au collisions, the binary collision scaled ${\pi }^0$ yield at high $p_T$ is suppressed by a factor of about 5 compared to the expectation from the yield of p+p collisions. Such a large suppression is in agreement with previous observations for light quark mesons and is consistent with the scenario that partons suffer considerable energy loss in the dense medium formed in central nucleus-nucleus collisions at RHIC.

   nucl-exPRC(2009)·33 citations
4. 04*

   Photon Physics in ALICE

   D.Peressounko🇷🇺 · Y.Kharlov (for the ALICE collaboration)🇷🇺

   We give an overview of photon physics which will be studied by the ALICE experiment in proton-proton and heavy ion collisions at LHC. We compare properties of ALICE photon detectors and estimate their ability to measure neutral meson and direct photon spectra as well as gamma-hadron and gamma-jet correlations in pp and Pb+Pb collisions.

   nucl-exNPA(2009)·1 citation
5. 05*

   Viscosity of the matter created in nucleus-nucleus collisions at the SPS measured via two-pion interferometry

   The CERES Collaboration

   This paper has been withdrawn by the authors because the formula used to fit the pion source radii accounted for only one of the two effects of finite viscosity, and because a mistake in interpreting RHIC data was discovered.

   nucl-ex3 citations
6. 06*

   Neutron-proton elliptic flow in Au + Au

   W. Trautmann🇩🇪 · M. Chartier🇬🇧 · Y. Leifels🇩🇪 · R.C. Lemmon🇬🇧 · Q. Li🇨🇳 · J. Lukasik🇵🇱 · A. Pagano🇮🇹 · P. Pawlowski🇵🇱 · P. Russotto🇮🇹 · P.Z. Wu🇬🇧

   The elliptic flow of neutrons, protons and light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. Preliminary results from a study of the existing FOPI/LAND data for 197Au + 197Au collisions at 400 A MeV with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to (rho/rho_0)^gamma with gamma = 0.9 +- 0.3.

   nucl-ex6 citations
7. 07*

   Results from the commissioning of the ALICE Inner Tracking System with cosmics

   Francesco Prino (INFN Torino) (for the ALICE collaboration)🇮🇹

   The Inner Tracking System (ITS) is the detector of the ALICE central barrel located closest to the beam axis and it is therefore a key detector for tracking and vertexing performance. Here, the main results from the ITS commissioning with atmospheric muons in 2008 are presented, focusing in particular on the detector operation and calibration and on the methods developed for the alignment of the ITS detectors using reconstructed tracks.

   nucl-exNPA(2009)·4 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.