Eur. Phys. J. C (2009) 61: 597-601
https://doi.org/10.1140/epjc/s10052-009-0960-z

Regular Article - Experimental Physics

Modified fragmentation function in heavy ion collisions at RHIC via direct γ-jet measurements

Physics Department, Cyclotron Institute, Texas A&M University, College Station, TX, 77843, USA

^* e-mail: ahamed@tamu.edu

Received: 8 September 2008
Revised: 9 December 2008
Published online: 25 February 2009

Abstract

The presented results are the first measurements at RHIC for direct γ-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density of the medium through the medium-induced modification of high-p _T parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8<p _T <16 GeV) with away-side charged hadrons of transverse momentum (3<p _T <6 GeV/c) have been measured over a broad range of centrality for Au+Au collisions and p+p collisions at  GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum Detector is used to discriminate between the direct photons and photons from the decays of high p _T π ⁰. The per-trigger away-side yield of direct γ is smaller than from π ⁰ trigger at the same centrality class. Within the current uncertainty the I _CP of direct γ and π ⁰ are similar.