Measurement of jet-medium interactions via direct photon-hadron correlations in Au+Au and +Au collisions at GeV

Acharya, U.*; Hasegawa, Shoichi   ; Imai, Kenichi*; Nagamiya, Shoji*; Sako, Hiroyuki   ; Sato, Susumu  ; Tanida, Kiyoshi   ; PHENIX Collaboration*; 572 of others*

We present direct photon-hadron correlations in 200 GeV/A AuAu, Au and collisions, for direct photon from 5 - 12 GeV/, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in 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 AuAu compared to and Au. As the momentum fraction decreases, the yield of hadrons in AuAu increases to an excess over the yield in collisions. The excess is at large angles and at low hadron 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.