| Abstract: | 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. |
REGISTER
You have a question or message about this article?
Ask the community and write a message in the forum.