Measurement of jet-medium interactions via direct photon-hadron correlations in Au$+$Au and $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This study measures how jets interact with the quark-gluon plasma in heavy-ion collisions by analyzing direct photon-hadron correlations, revealing suppression and enhancement patterns indicative of medium response effects.

Contribution

It provides the first detailed measurement of jet-medium interactions via direct photon-hadron correlations across different collision systems at 200 GeV.

Findings

No significant jet modification in d+Au collisions.

Suppression of high-momentum hadrons in Au+Au collisions.

Excess of low-momentum hadrons at large angles in Au+Au, indicating medium response.

Abstract

We present direct photon-hadron correlations in 200 GeV/A Au$+$Au, $d$$+$Au and $p$$+$$p$ collisions, for direct photon $p_T$ from 5--12 GeV/$c$, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in $d$$+$Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au$+$Au compared to $p$$+$$p$ and $d$$+$Au. As the momentum fraction decreases, the yield of hadrons in Au$+$Au increases to an excess over the yield in $p$$+$$p$ collisions. The excess is at large angles and at low hadron $p_T$ and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.