Campus Units

Physics and Astronomy

Document Type

Article

Publication Version

Published Version

Publication Date

10-9-2012

Journal or Book Title

Physical Review Letters

Volume

109

Issue

15

First Page

152302

DOI

10.1103/PhysRevLett.109.152302

Abstract

We report the measurement of direct photons at midrapidity in Au + Au collisions at root s(NN) = 200 GeV. The direct photon signal was extracted for the transverse momentum range of 4 GeV/c < pT < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive photon sample. The direct photon nuclear modification factor R-AA was calculated as a function of p(T) for different Au + Au collision centralities using the measured p + p direct photon spectrum and compared to theoretical predictions. R-AA was found to be consistent with unity for all centralities over the entire measured pT range. Theoretical models that account for modifications of initial direct photon production due to modified parton distribution functions in Au and the different isospin composition of the nuclei predict a modest change of R-AA from unity. They are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.

Comments

This is an article from Physical Review Letters 109 (2012): 152302-1, doi:10.1103/PhysRevLett.109.152302. Posted with permission.

Copyright Owner

American Physical Society

Language

en

File Format

application/pdf

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