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Enhanced production of direct photons in Au+Au collisions at sqrt(s_NN)=200 GeV and implications for the initial temperature

A. Adare S. Afanasiev C. Aidala N.N. Ajitanand Y. Akiba H. Al-Bataineh J. Alexander A. Al-Jamel K. Aoki Laurent Aphecetche 1 R. Armendariz S.H. Aronson J. Asai E. T. Atomssa 2 R. Averbeck T.C. Awes B. Azmoun V. Babintsev G. Baksay L. Baksay A. Baldisseri 3 K.N. Barish P.D. Barnes B. Bassalleck S. Bathe S. Batsouli V. Baublis F. Bauer A. Bazilevsky S. Belikov R. Bennett Y. Berdnikov A.A. Bickley M.T. Bjorndal J.G. Boissevain H. Borel 3 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 B.S. Chang J.-L. Charvet 3 S. Chernichenko J. Chiba C.Y. Chi M. Chiu I.J. Choi T. Chujo P. Chung A. Churyn V. Cianciolo C.R. Cleven Y. Cobigo 3 B.A. Cole M.P. Comets 4 P. Constantin M. Csan'Ad T. Cs¨org˝o T. Dahms K. Das G. David M.B. Deaton K. Dehmelt H. Delagrange 1 A. Denisov D. d'Enterria A. Deshpande E.J. Desmond O. Dietzsch A. Dion M. Donadelli J.L. Drachenberg O. Drapier 2 A. Drees A.K. Dubey A. Durum V. Dzhordzhadze Y.V. Efremenko J. Egdemir F. Ellinghaus W.S. Emam A. Enokizono H. En'Yo B. Espagnon 4 S. Esumi K.O. Eyser D.E. Fields M. Finger M. Finger Jr. F. Fleuret 2 S.L. Fokin B. Forestier 5 Z. Fraenkel J.E. Frantz A. Franz A.D. Frawley K. Fujiwara Y. Fukao S.-Y. Fung T. Fusayasu S. Gadrat 5 I. Garishvili F. Gastineau 1 Marie Germain 1 A. Glenn H. Gong M. Gonin 2 J. Gosset 3 Y. Goto R. Granier de Cassagnac 2 N. Grau S.V. Greene M. Grosse Perdekamp T. Gunji H.-°a. Gustafsson T. Hachiya A. Hadj Henni 1 C. Haegemann J.S. Haggerty M.N. Hagiwara H. Hamagaki R. Han H. Harada E.P. Hartouni K. Haruna M. Harvey E. Haslum K. Hasuko R. Hayano M. Heffner T.K. Hemmick T. Hester J.M. Heuser X. He H. Hiejima J.C. Hill R. Hobbs M. Hohlmann M. Holmes W. Holzmann K. Homma B. Hong T. Horaguchi D. Hornback M.G. Hur T. Ichihara K. Imai M. Inaba Y. Inoue 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 4 F. Kajihara S. Kametani N. Kamihara J. Kamin M. Kaneta J.H. Kang H. Kanou T. Kawagishi D. Kawall A.V. Kazantsev Steven Kelly A. Khanzadeev J. Kikuchi D.H. Kim D.J. Kim E. Kim Y.-S. Kim E. Kinney A. Kiss E. Kistenev A. Kiyomichi J. Klay C. Klein-Boesing L. Kochenda V. Kochetkov B. Komkov M. Konno D. Kotchetkov A. Kozlov A. Kr'Al A. Kravitz P.J. Kroon J. Kubart G.J. Kunde N. Kurihara K. Kurita M.J. Kweon Y. Kwon G.S. Kyle R. Lacey Y.-S. Lai J.G. Lajoie A. Lebedev Y. Le Bornec 4 S. Leckey D.M. Lee M.K. Lee T. Lee M.J. Leitch M.A.L. Leite B. Lenzi H. Lim T. Liˇska A. Litvinenko M.X. Liu X. Li X.H. Li B. Love D. Lynch C.F. Maguire Y.I. Makdisi A. Malakhov M.D. Malik V.I. Manko Y. Mao L. Maˇsek H. Masui F. Matathias M.C. Mccain M. Mccumber P.L. Mcgaughey Y. Miake P. Mikeˇs K. Miki T.E. Miller A. Milov S. Mioduszewski G.C. Mishra M. Mishra J.T. Mitchell M. Mitrovski A. Morreale D.P. Morrison J.M. Moss T.V. Moukhanova D. Mukhopadhyay J. Murata S. Nagamiya Y. Nagata J.L. Nagle M. Naglis I. Nakagawa Y. Nakamiya T. Nakamura K. Nakano J. Newby M. Nguyen B.E. Norman A.S. Nyanin J. Nystrand E. O'Brien S.X. Oda C.A. Ogilvie H. Ohnishi I.D. Ojha H. Okada K. Okada M. Oka O.O. Omiwade A. Oskarsson I. Otterlund M. Ouchida K. Ozawa R. Pak 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 3 V. Peresedov D.Yu. Peressounko C. Pinkenburg R.P. Pisani M.L. Purschke A.K. Purwar H. Qu J. Rak A. Rakotozafindrabe 2 I. Ravinovich K.F. Read S. Rembeczki M. Reuter K. Reygers V. Riabov Y. Riabov G. Roche 5 A. Romana 2 M. Rosati S.S.E. Rosendahl P. Rosnet 5 P. Rukoyatkin V.L. Rykov S.S. Ryu B. Sahlmueller N. Saito T. Sakaguchi S. Sakai H. Sakata V. Samsonov H.D. Sato S. Sato S. Sawada J. Seele R. Seidl V. Semenov R. Seto D. Sharma T.K. Shea I. Shein A. Shevel T.-A. Shibata K. Shigaki M. Shimomura T. Shohjoh K. Shoji A. Sickles C.L. Silva D. Silvermyr C. Silvestre 3 K.S. Sim C.P. Singh V. Singh S. Skutnik M. Slunecka W.C. Smith A. Soldatov R.A. Soltz W.E. Sondheim S.P. Sorensen I.V. Sourikova F. Staley 3 P.W. Stankus E. Stenlund M. Stepanov A. Ster S.P. Stoll T. Sugitate C. Suire 4 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 A. Toia J. Tojo L. Tom'Aˇsek H. Torii R.S. Towell V.-N. Tram 2 I. Tserruya Y. Tsuchimoto S.K. Tuli H. Tydesj¨o N. Tyurin C. Vale H. Valle H.W. van Hecke J. Velkovska R. Vertesi A.A. Vinogradov M. Virius V. Vrba E. Vznuzdaev M. Wagner D. Walker X.R. Wang Y. Watanabe J. Wessels S.N. White N. Willis 4 D. Winter C.L. Woody M. Wysocki W. Xie Y.L. Yamaguchi A. Yanovich Z. Yasin J. Ying S. Yokkaichi G.R. Young I. Younus I.E. Yushmanov W.A. Zajc O. Zaudtke C. Zhang S. Zhou J. Zim'Anyi L. Zolin
Abstract : The production of low mass e+e- pairs for m_{e+e-} < 300 MeV/c^2 and 1 < p_T <5 GeV/c is measured in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. Enhanced e+e- pair yield above hadronic sources is observed in Au+Au collisions. Treating the excess as internal conversion of direct photons, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess over p+p is exponential in p_T}, with inverse slope T = 221 +/- 23 (stat) +/- 18 (syst) MeV. Hydrodynamical models with initial temperatures T_init ~ 300-600 MeV at times of 0.6 - 0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition at ~ 170 MeV.
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A. Adare, S. Afanasiev, C. Aidala, N.N. Ajitanand, Y. Akiba, et al.. Enhanced production of direct photons in Au+Au collisions at sqrt(s_NN)=200 GeV and implications for the initial temperature. Physical Review Letters, American Physical Society, 2010, 104, pp.132301. ⟨10.1103/PhysRevLett.104.132301⟩. ⟨in2p3-00277382⟩

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