Measurement of Direct Photons in Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV - INSPIRE

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Measurement of Direct Photons in Au+Au Collisions at $\sqrt{s_{NN}} = 200$ GeV

PHENIX

Collaboration

May, 2012

7 pages

Published in:

Phys.Rev.Lett. 109 (2012) 152302

e-Print:

1205.5759 [nucl-ex]

DOI:

10.1103/PhysRevLett.109.152302

Experiments:

BNL-RHIC-PHENIX

View in:

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Abstract: (arXiv)

We report the measurement of direct photons at midrapidity in Au+Au collisions at sqrt{s_NN} = 200 GeV. The direct photon signal was extracted for the transverse-momentum range of 4 GeV/c < p_T < 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 p_T 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 and 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.

Note:

PHENIX Collaboration, 346 authors, 8 pages, 4 figures, 1 table. Submitted to Phys. Rev. Lett. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

25.75.Dw
photon: direct production
quark gluon: plasma
heavy ion: scattering
gold
cross section: measured
PHENIX
photon: yield
nuclear matter: effect
transverse momentum: dependence

References(20)

Figures(1)

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