Detailed measurement of the e(+)e(-) pair continuum in p plus p and Au plus Au collisions at root s(NN)=200 GeV and implications for direct photon production

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, Nouicer R, 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, Takag

Abstract

PHENIX has measured the e(+)e(-) pair continuum in root s(NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e(+)e(-) yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c (c) over bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7 +/- 0.4(stat) +/- 1.5(syst) +/- 0.9(model). At low mass (m(ee) < 0.3 GeV/c(2)) and high p(T) (1 < p(T) < 5 GeV/c) an enhanced e(+)e(-) pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p(T), with inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar or equal to 300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p(T) < 1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T similar or equal to 100 MeV. Theoretical models underpredict the low-mass, low-p(T) enhancement.