Direct photon-hadron correlation measurement and a way towards photon-triggered jets at RHIC

Nihar Ranjan Sahoo

doi:10.1088/1742-6596/832/1/012003

Abstract

We report the results of γdir- and π0–hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity with respect to high-pT γdir and π0 in central Au+Au collisions are compared with p+p collisions. Within uncertainties, the same dependence of the suppression is observed for γdir- and π0- triggers. The results are compared with energy-loss model predictions. The γ − jet measurements can provide further understanding on the redistribution of in-medium energy loss. Ongoing γ − jet studies in the STAR experiment are also discussed.

Highlights

The azimuthal correlation of charged hadrons with respect to a direct-photon trigger was proposed as a promising probe to study the mechanisms of parton energy loss [1]
Since a γdirtrigger escapes without interacting with the medium, it approximates the initial energy of the recoil parton, which is subject to medium modifications
A detailed discussion about the transverse shower profile (TSP) method and experimental techniques used in this analysis can be found in Ref. [6, 7]

Summary

Introduction

The azimuthal correlation of charged hadrons with respect to a direct-photon (γdir) trigger was proposed as a promising probe to study the mechanisms of parton energy loss [1]. Since a γdirtrigger escapes without interacting with the medium, it approximates the initial energy of the recoil parton, which is subject to medium modifications. The recoil parton of a γdir trigger is a quark in leading-order QCD processes, whereas that of a high-pT π0 trigger can be a quark or a gluon. The comparison between the suppression of per-trigger away-side associated yields of γdir to those of π0 triggers should exhibit differences due to both the color-factor dependence and the path-length dependence of energy loss

STAR Detectors and Experimental techniques

Results: γdirand π0–hadron azimuthal correlation