Measurement of Direct Photons inAu+AuCollisions atsNN=200  GeV

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

doi:10.1103/physrevlett.109.152302

Abstract

We report the measurement of direct photons at midrapidity in Au+Au collisions at sNN=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 RAA was calculated as a function of pT for different Au+Au collision centralities using the measured p+p direct photon spectrum and compared to theoretical predictions. RAA 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 RAA 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.Received 27 May 2012DOI:https://doi.org/10.1103/PhysRevLett.109.152302© 2012 American Physical Society

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