# Quark Matter 2014 - XXIV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

19-24 May 2014
Europe/Zurich timezone

## Measurements of direct-photon-hadron correlations and direct-photon azimuthal anisotropy by STAR

19 May 2014, 16:30
20m

### helium

Contributed Talk Electromagnetic Probes

### Speaker

Dr Ahmed M. Hamed (University of Mississippi, Texas A&M University)

### Description

Many observations have indicated that the fragmentation functions in nucleus-nucleus collisions are softened compared to that in proton-proton collisions. Different theoretical models have been proposed in order to describe the observed phenomena. For a deeper insight into the underlying physics and better constraints for the extracted parameters of the medium formed in nucleus-nucleus collisions, a calibrated probe is needed. Direct photons act as such probes, providing experimental tools to explore energy loss of hard-scattered patrons. We report systematic studies of azimuthal correlations of charged hadrons with respect to a direct-photon trigger in p+p and Au+Au collisions, using new data collected in 2008, 2009, and 2011. The nuclear modification factor of coincidence rate, $I_{AA}$, will be shown. We also report direct-photon azimuthal anisotropy as a function of transverse momentum at mid-rapidity with event plane reconstructed from particles at forward rapidity in Au+Au collisions using the STAR detector at RHIC. We discuss the results in the scope of current theoretical models.
On behalf of collaboration: STAR

### Primary author

Dr Ahmed M. Hamed (University of Mississippi, Texas A&M University)

### Presentation Materials

 Direct_photon_QM-2014_Final.pdf Direct_photon_QM-2014_Final.pptx