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

S. Afanasiev , C. Aidala , N. N. Ajitanand , Y. Akiba , A. Al-Jamel , J. Alexander , K. Aoki , L. Aphecetche

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R. Armendariz S. H. Aronson R. Averbeck T. C. Awes B. Azmoun V. Babintsev A. Baldisseri K. N. Barish P. D. Barnes B. Bassalleck S. Bathe S. Batsouli V. Baublis F. Bauer A. Bazilevsky S. Belikov R. Bennett Y. Berdnikov M. T. Bjorndal J. G. Boissevain H. Borel K. Boyle M. L. Brooks D. S. Brown D. Bucher H. Buesching V. Bumazhnov G. Bunce J. M. Burward-Hoy S. Butsyk S. Campbell J.-S. Chai S. Chernichenko C. Y. Chi J. Chiba M. Chiu I. J. Choi T. Chujo V. Cianciolo C. R. Cleven Y. Cobigo B. A. Cole M. P. Comets M. Connors P. Constantin M. Csan\'ad T. Cs\"org\H{o} T. Dahms K. Das G. David H. Delagrange A. Denisov D. d'Enterria A. Deshpande E. J. Desmond O. Dietzsch A. Dion J. L. Drachenberg O. Drapier A. Drees A. K. Dubey A. Durum V. Dzhordzhadze Y. V. Efremenko J. Egdemir A. Enokizono H. En'yo B. Espagnon S. Esumi D. E. Fields F. Fleuret S. L. Fokin B. Forestier Z. Fraenkel J. E. Frantz A. Franz A. D. Frawley Y. Fukao S.-Y. Fung S. Gadrat F. Gastineau M. Germain A. Glenn M. Gonin J. Gosset Y. Goto R. Granier de Cassagnac N. Grau S. V. Greene M. Grosse Perdekamp T. Gunji H.-{\AA}. Gustafsson T. Hachiya A. Hadj Henni J. S. Haggerty M. N. Hagiwara H. Hamagaki H. Harada E. P. Hartouni K. Haruna M. Harvey E. Haslum K. Hasuko R. Hayano X. He M. Heffner T. K. Hemmick J. M. Heuser H. Hiejima J. C. Hill R. Hobbs M. Holmes W. Holzmann K. Homma B. Hong T. Horaguchi M. G. Hur T. Ichihara H. Iinuma K. Imai J. Imrek M. Inaba D. Isenhower L. Isenhower M. Ishihara T. Isobe M. Issah A. Isupov B. V. Jacak J. Jia J. Jin O. Jinnouchi B. M. Johnson K. S. Joo D. Jouan F. Kajihara S. Kametani N. Kamihara M. Kaneta J. H. Kang T. Kawagishi A. V. Kazantsev S. Kelly A. Khanzadeev D. J. Kim E. Kim Y.-S. Kim E. Kinney \'A. Kiss E. Kistenev A. Kiyomichi C. Klein-Boesing L. Kochenda V. Kochetkov B. Komkov M. Konno D. Kotchetkov A. Kozlov P. J. Kroon G. J. Kunde N. Kurihara K. Kurita M. J. Kweon Y. Kwon G. S. Kyle R. Lacey J. G. Lajoie A. Lebedev Y. Le Bornec S. Leckey D. M. Lee M. K. Lee M. J. Leitch M. A. L. Leite X. H. Li H. Lim A. Litvinenko M. X. Liu C. F. Maguire Y. I. Makdisi A. Malakhov M. D. Malik V. I. Manko H. Masui F. Matathias M. C. McCain P. L. McGaughey Y. Miake T. E. Miller A. Milov S. Mioduszewski G. C. Mishra J. T. Mitchell D. P. Morrison J. M. Moss T. V. Moukhanova D. Mukhopadhyay J. Murata S. Nagamiya Y. Nagata J. L. Nagle M. Naglis T. Nakamura J. Newby M. Nguyen B. E. Norman A. S. Nyanin J. Nystrand E. O'Brien C. A. Ogilvie H. Ohnishi I. D. Ojha K. Okada O. O. Omiwade A. Oskarsson I. Otterlund K. Ozawa D. Pal A. P. T. Palounek V. Pantuev V. Papavassiliou J. Park W. J. Park S. F. Pate H. Pei J.-C. Peng H. Pereira V. Peresedov D. Yu. Peressounko C. Pinkenburg R. P. Pisani M. L. Purschke A. K. Purwar H. Qu J. Rak I. Ravinovich K. F. Read M. Reuter K. Reygers V. Riabov Y. Riabov G. Roche A. Romana M. Rosati S. S. E. Rosendahl P. Rosnet P. Rukoyatkin V. L. Rykov S. S. Ryu B. Sahlmueller N. Saito T. Sakaguchi S. Sakai V. Samsonov H. D. Sato S. Sato S. Sawada V. Semenov R. Seto D. Sharma T. K. Shea I. Shein T.-A. Shibata K. Shigaki M. Shimomura T. Shohjoh K. Shoji A. Sickles C. L. Silva D. Silvermyr K. S. Sim C. P. Singh V. Singh S. Skutnik W. C. Smith A. Soldatov R. A. Soltz W. E. Sondheim S. P. Sorensen I. V. Sourikova F. Staley P. W. Stankus E. Stenlund M. Stepanov A. Ster S. P. Stoll T. Sugitate C. Suire J. P. Sullivan J. Sziklai T. Tabaru S. Takagi E. M. Takagui A. Taketani K. H. Tanaka Y. Tanaka K. Tanida M. J. Tannenbaum A. Taranenko P. Tarj\'an T. L. Thomas M. Togawa J. Tojo H. Torii R. S. Towell V-N. Tram I. Tserruya Y. Tsuchimoto S. K. Tuli H. Tydesj\"o N. Tyurin C. Vale H. Valle H. W. van Hecke J. Velkovska R. V\'ertesi A. A. Vinogradov E. Vznuzdaev M. Wagner X. R. Wang Y. Watanabe J. Wessels S. N. White N. Willis D. Winter C. L. Woody M. Wysocki W. Xie A. Yanovich S. Yokkaichi G. R. Young I. Younus I. E. Yushmanov W. A. Zajc O. Zaudtke C. Zhang J. Zim\'anyi L. Zolin

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keywords photonsconsistentdirectmeasurementcentralitiescollisionsdifferentdirect-photon

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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.

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On the Role of Prompt Photons in the Anisotropic Emission of Direct Photons -- Direct Photons from Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV with IP-Glasma Initial Condition
hep-ph 2026-04 unverdicted novelty 4.0

Accounting for prompt photons in a viscous hydrodynamic model of Au+Au collisions explains the measured v2 and v3 of direct photons, with good agreement in mid-central collisions but centrality-dependent discrepancies.