Enhanced Production of Direct Photons in Au plus Au Collisions at root s(NN)=200 GeV and Implications for the Initial Temperature

Adare A, Afanasiev S, Aidala C, Ajitanand NN, Akiba Y, Al-Bataineh H, Alexander J, Al-Jamel A, Aoki K, Aphecetche L, Armendariz R, Aronson SH, Asai J, Atomssa ET, Averbeck R, Awes TC, Azmoun B, Babintsev V, Baksay G, Baksay L, Baldisseri A, Barish KN, Barnes PD, Bassalleck B, Bathe S, Batsouli S, Baublis V, Bauer F, Bazilevsky A, Belikov S, Bennett R, Berdnikov Y, Bickley AA, Bjorndal MT, Boissevain JG, Borel H, Boyle K, Brooks ML, Brown DS, Bucher D, Buesching H, Bumazhnov V, Bunce G, Burward-Hoy JM, Butsyk S, Campbell S, Chai JS, Chang BS, Charvet JL, Chernichenko S, Chiba J, Chi CY, Chiu M, Choi IJ, Chujo T, Chung P, Churyn A, Cianciolo V, Cleven CR, Cobigo Y, Cole BA, Comets MP, Constantin P, Csanad M, Csorgo T, Dahms T, Das K, David G, Deaton MB, Dehmelt K, Delagrange H, Denisov A, d'Enterria D, Deshpande A, Desmond EJ, Dietzsch O, Dion A, Donadelli M, Drachenberg JL, Drapier O, Drees A, Dubey AK, Durum A, Dzhordzhadze V, Efremenko YV, Egdemir J, Ellinghaus F, Emam WS, Enokizono A, En'yo H, Espagnon B, Esumi S, Eyser KO, Fields DE, Finger M, Finger M, Fleuret F, Fokin SL, Forestier B, Fraenkel Z, Frantz JE, Franz A, Frawley AD, Fujiwara K, Fukao Y, Fung SY, Fusayasu T, Gadrat S, Garishvili I, Gastineau F, Germain M, Glenn A, Gong H, Gonin M, Gosset J, Goto Y, de Cassagnac RG, Grau N, Greene SV, Perdekamp MG, Gunji T, Gustafsson HA, Hachiya T, Henni AH, Haegemann C, Haggerty JS, Hagiwara MN, Hamagaki H, Han R, Harada H, Hartouni EP, Haruna K, Harvey M, Haslum E, Hasuko K, Hayano R, Heffner M, Hemmick TK, Hester T, Heuser JM, He X, Hiejima H, Hill JC, Hobbs R, Hohlmann M, Holmes M, Holzmann W, Homma K, Hong B, Horaguchi T, Hornback D, Hur MG, Ichihara T, Imai K, Inaba M, Inoue Y, Isenhower D, Isenhower L, Ishihara M, Isobe T, Issah M, Isupov A, Jacak BV, Jia J, Jin J, Jinnouchi O, Johnson BM, Joo KS, Jouan D, Kajihara F, Kametani S, Kamihara N, Kamin J, Kaneta M, Kang JH, Kanou H, Kawagishi T, Kawall D, Kazantsev AV, Kelly S, Khanzadeev A, Kikuchi J, Kim DH, Kim DJ, Kim E, Kim YS, Kinney E, Kiss A, Kistenev E, Kiyomichi A, Klay J, Klein-Boesing C, Kochenda L, Kochetkov V, Komkov B, Konno M, Kotchetkov D, Kozlov A, Kral A, Kravitz A, Kroon PJ, Kubart J, Kunde GJ, Kurihara N, Kurita K, Kweon MJ, Kwon Y, Kyle GS, Lacey R, Lai YS, Lajoie JG, Lebedev A, Le Bornec Y, Leckey S, Lee DM, Lee MK, Lee T, Leitch MJ, Leite MAL, Lenzi B, Lim H, Liska T, Litvinenko A, Liu MX, Li X, Li XH, Love B, Lynch D, Maguire CF, Makdisi YI, Malakhov A, Malik MD, Manko VI, Mao Y, Masek L, Masui H, Matathias F, McCain MC, McCumber M, McGaughey PL, Miake Y, Mikes P, Miki K, Miller TE, Milov A, Mioduszewski S, Mishra GC, Mishra M, Mitchell JT, Mitrovski M, Morreale A, Morrison DP, Moss JM, Moukhanova TV, Mukhopadhyay D, Murata J, Nagamiya S, Nagata Y, Nagle JL, Naglis M, Nakagawa I, Nakamiya Y, Nakamura T, Nakano K, Newby J, Nguyen M, Norman BE, Nyanin AS, Nystrand J, O'Brien E, Oda SX, Ogilvie CA, Ohnishi H, Ojha ID, Okada H, Okada K, Oka M, Omiwade OO, Oskarsson A, Otterlund I, Ouchida M, Ozawa K, Pak R, Pal D, Palounek APT, Pantuev V, Papavassiliou V, Park J, Park WJ, Pate SF, Pei H, Peng JC, Pereira H, Peresedov V, Peressounko DY, Pinkenburg C, Pisani RP, Purschke ML, Purwar AK, Qu H, Rak J, Rakotozafindrabe A, Ravinovich I, Read KF, Rembeczki S, Reuter M, Reygers K, Riabov V, Riabov Y, Roche G, Romana A, Rosati M, Rosendahl SSE, Rosnet P, Rukoyatkin P, Rykov VL, Ryu SS, Sahlmueller B, Saito N, Sakaguchi T, Sakai S, Sakata H, Samsonov V, Sato HD, Sato S, Sawada S, Seele J, Seidl R, Semenov V, Seto R, Sharma D, Shea TK, Shein I, Shevel A, Shibata TA, Shigaki K, Shimomura M, Shohjoh T, Shoji K, Sickles A, Silva CL, Silvermyr D, Silvestre C, Sim KS, Singh CP, Singh V, Skutnik S, Slunecka M, Smith WC, Soldatov A, Soltz RA, Sondheim WE, Sorensen SP, Sourikova IV, Staley F, Stankus PW, Stenlund E, Stepanov M, Ster A, Stoll SP, Sugitate T, Suire C, Sullivan JP, Sziklai J, Tabaru T, Takagi S, Takagui EM, Take

Abstract

The production of e(+)e(-) pairs for m(e+e-) < 0.3 GeV/c(2) and 1< p(T) < 5 GeV/c is measured in p + p and Au + Au collisions at root s(NN) = 200 GeV. An enhanced yield above hadronic sources is observed. Treating the excess as photon internal conversions, the invariant yield of direct photons is deduced. In central Au + Au collisions, the excess of the direct photon yield over p + p is exponential in transverse momentum, with an inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar to 300-600 MeV at times of similar to 0.6-0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at similar to 170 MeV.