# Quark Matter 2015 - XXV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

September 27, 2015 to October 3, 2015
Kobe, Fashion Mart, Japan
Japan timezone

## Direct-photon+hadron correlations to study parton energy loss with the STAR experiment

Sep 29, 2015, 11:30 AM
20m
KFM Hall "IO"

### KFM Hall "IO"

Contributed talk Jets and High pT Hadrons

### Speaker

Dr Nihar Sahoo (Texas A & M University)

### Description

Photons are valuable probes of the QCD plasma due to their lack of color and electric charge. Direct photons ($\gamma_{dir}$), those produced during the collision rather than from decays of hadrons, are not affected by the medium.The study of direct-photon-triggered away-side jets can give information about the energy loss of the away-side parton while traversing through the medium. On the other hand, comparison between the suppression of $\gamma_{dir}$- and $\pi^{0}$- triggered away-side hadron yields can give information about the path-length and color-factor dependence of parton energy loss. We report new results of $\gamma_{dir}$+hadron and $\pi^{0}$+hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment from years 2011 and 2009 of data taking, respectively. The charged-hadron per-trigger yields at mid-rapidity $(|\eta| < 1)$ and for transverse momenta $p_{T}^{assoc} > 1.2$ GeV/c associated with $\gamma_{dir}$ and $\pi^{0}$ (for triggers $|\eta| <$0.9, 12 $< p_{T}^{trig} <$ 20 GeV/c) in central Au+Au collisions are compared with p+p collisions. With this new low $p_{T}^{assoc}$ cut, we see evidence for the recovery of the lost energy in the low-momentum range for the constituents of the jet.The $z_{T}$ ($= \frac{p_{T}^{assoc}}{p_{T}^{trig}}$) dependence, now extending down to $z_{T}$=0.1, of the suppression of the away-side associated yields is presented. The dependence of the suppression on both $p_{T}^{assoc}$ and $p_{T}^{trig}$ is also discussed. Finally, these results are compared with various model predictions.
On behalf of collaboration: STAR

### Primary author

Dr Nihar Sahoo (Texas A & M University)