Measurement of Direct Photons in Au+Au Collisions at sqrt(s_NN) = 200 GeV

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. T...

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Veröffentlicht in:	arXiv.org 2012-05
Hauptverfasser:	Ajitanand, N N, Aoki, K, Aphecetche, L, Averbeck, R, Baldisseri, A, Bauer, F, Bennett, R, Berdnikov, Y, Borel, H, Bumazhnov, V, Burward-Hoy, J M, Butsyk, S, Campbell, S, Chiba, J, Cole, B A, Connors, M, Csanád, M, Csörgő, T, Dahms, T, Denisov, A, Dietzsch, O, Dion, A, Efremenko, Y V, Egdemir, J, Enokizono, A, Frantz, J E, S -Y Fung, Gosset, J, R Granier de Cassagnac, Gunji, T, A Hadj Henni, Haggerty, J S, Harada, H, Haruna, K, Hasuko, K, Hayano, R, X He, Heffner, M, Hemmick, T K, Horaguchi, T, Hur, M G, Ichihara, T, Imai, K, Isenhower, L, Issah, M, Jinnouchi, O, Johnson, B M, Jouan, D, Kametani, S, Kaneta, M, Kim, D J, Kiss, Á, Kistenev, E, Kiyomichi, A, Klein-Boesing, C, Kochenda, L, Konno, M, Kozlov, A, Kweon, M J, Kwon, Y, Kyle, G S, Matathias, F, Miake, Y, Morrison, D P, Murata, J, Nagle, J L, Nystrand, J, Ogilvie, C A, Okada, K, Oskarsson, A, Pantuev, V, Park, W J, D Yu Peressounko, Ravinovich, I, Reygers, K, Riabov, V, Sahlmueller, B, Sakaguchi, T, Sato, S, Sawada, S, Shea, T K, Shein, I, Sim, K S, Singh, V, Soltz, R A, Takagui, E M, Tanaka, K H, Tannenbaum, M J, Tojo, J, V-N Tram, Tserruya, I, Tydesjö, H, Valle, H, Vinogradov, A A, Wagner, M, White, S N, Yanovich, A, Yokkaichi, S, Young, G R, Younus, I
Format:	Artikel
Sprache:	eng
Schlagworte:	Bremsstrahlung Collisions Distribution functions Mathematical models Partons Photons Physics - Nuclear Experiment Quark-gluon plasma Quarks Rangefinding Statistical analysis Unity
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Zusammenfassung:	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.
ISSN:	2331-8422
DOI:	10.48550/arxiv.1205.5759