Photon-hadron jet correlations in p plus p and Au plus Au collisions at s(NN)=200 GeV

Adare, Andrew
Belikov, Sergey
Ogilvie, Craig
Constantin, Paul
Grau, Nathan
Hill, John
Kempel, Todd
Lajoie, John
Lebedev, Alexandre
Ogilvie, Craig
Pei, H.
Rak, Jan
Rosati, Marzia
Semenov, Alexey
Skutnik, S.
Vale, Carla
Wei, Feng
et al.
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We report the observation at the Relativistic Heavy Ion Collider of suppression of back-to-back correlations in the direct photon+jet channel in Au+Au relative to p+p collisions. Two-particle correlations of direct photon triggers with associated hadrons are obtained by statistical subtraction of the decay photon-hadron (gamma-h) background. The initial momentum of the away-side parton is tightly constrained, because the parton-photon pair exactly balance in momentum at leading order in perturbative quantum chromodynamics, making such correlations a powerful probe of the in-medium parton energy loss. The away-side nuclear suppression factor, I-AA, in central Au+Au collisions, is 0.32 +/- 0.12(stat)+/- 0.09(syst) for hadrons of 3 < p(T)(h)< 5 in coincidence with photons of 5 < p(T)(gamma)< 15 GeV/c. The suppression is comparable to that observed for high-p(T) single hadrons and dihadrons. The direct photon associated yields in p+p collisions scale approximately with the momentum balance, z(T)equivalent to p(T)(h)/p(T)(gamma), as expected for a measurement of the away-side parton fragmentation function. We compare to Au+Au collisions for which the momentum balance dependence of the nuclear modification should be sensitive to the path-length dependence of parton energy loss.

<p>This article is published as Adare, A., S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander et al. "Photon-hadron jet correlations in p+ p and Au+ Au collisions at s NN= 200 GeV." <em>Physical Review C</em> 80, no. 2 (2009): 024908. DOI:<a href="" target="_blank">10.1103/PhysRevC.80.024908</a>. Posted with permission.</p>