/ Experiment-Nucl arXiv:0912.0244


Detailed measurement of the $e^+ e^-$ pair continuum in $p+p$ and Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and implications for direct photon production


Adare, A. ; Afanasiev, S. ; Aidala, C. ; Ajitanand, N.N. ; Akiba, Y. ; Al-Bataineh, H. ; Alexander, J. ; Al-Jamel, A. ; Aoki, K. ; Aphecetche, L. ; Armendariz, R. ; Aronson, S.H. ; Asai, J. ; Atomssa, E.T. ; Averbeck, R. ; Awes, T.C. ; Azmoun, B. ; Babintsev, V. ; Baksay, G. ; Baksay, L. ; Baldisseri, A. ; Barish, K.N. ; Barnes, P.D. ; Bassalleck, B. ; Bathe, S. ; Batsouli, S. ; Baublis, V. ; Bauer, F. ; Bazilevsky, A. ; Belikov, S. ; Bennett, R. ; Berdnikov, Y. ; Bickley, A.A. ; Bjorndal, M.T. ; Boissevain, J.G. ; Borel, H. ; Boyle, K. ; Brooks, M.L. ; Brown, D.S. ; Bucher, D. ; Buesching, H. ; Bumazhnov, V. ; Bunce, G. ; Burward-Hoy, J.M. ; Butsyk, S. ; Campbell, S. ; Chai, J.-S. ; Chang, B.S. ; Charvet, J.-L. ; Chernichenko, S. ; Chiba, J. ; Chi, C.Y. ; Chiu, M. ; Choi, I.J. ; Chujo, T. ; Chung, P. ; Churyn, A. ; Cianciolo, V. ; Cleven, C.R. ; Cobigo, Y. ; Cole, B.A. ; Comets, M.P. ; Constantin, P. ; Csanad, M. ; Csorgo, T. ; Dahms, T. ; Das, K. ; David, G. ; Deaton, M.B. ; Dehmelt, K. ; Delagrange, H. ; Denisov, A. ; d'Enterria, D. ; Deshpande, A. ; Desmond, E.J. ; Dietzsch, O. ; Dion, A. ; Donadelli, M. ; Drachenberg, J.L. ; Drapier, O. ; Drees, A. ; Dubey, A.K. ; Durum, A. ; Dzhordzhadze, V. ; Efremenko, Y.V. ; Egdemir, J. ; Ellinghaus, F. ; Emam, W.S. ; Enokizono, A. ; En'yo, H. ; Espagnon, B. ; Esumi, S. ; Eyser, K.O. ; Fields, D.E. ; Finger, M., Jr. ; Finger, M. ; Fleuret, F. ; Fokin, S.L. ; Forestier, B. ; Fraenkel, Z. ; Frantz, J.E. ; Franz, A. ; Frawley, Anthony D. ; Fujiwara, K. ; Fukao, Y. ; Fung, S.-Y. ; Fusayasu, T. ; Gadrat, S. ; Garishvili, I. ; Gastineau, F. ; Germain, M. ; Glenn, A. ; Gong, H. ; Gonin, M. ; Gosset, J. ; Goto, Y. ; Granier de Cassagnac, R. ; Grau, N. ; Greene, S.V. ; Grosse Perdekamp, M. ; Gunji, T. ; Gustafsson, H.-A. ; Hachiya, T. ; Hadj Henni, A. ; Haegemann, C. ; Haggerty, J.S. ; Hagiwara, M.N. ; Hamagaki, H. ; Han, R. ; Harada, H. ; Hartouni, Edward P. ; Haruna, K. ; Harvey, M. ; Haslum, E. ; Hasuko, K. ; Hayano, R. ; Heffner, M. ; Hemmick, T.K. ; Hester, T. ; Heuser, J.M. ; He, X. ; Hiejima, H. ; Hill, J.C. ; Hobbs, R. ; Hohlmann, M. ; Holmes, M. ; Holzmann, W. ; Homma, K. ; Hong, B. ; Horaguchi, T. ; Hornback, D. ; Hur, M.G. ; Ichihara, T. ; Imai, K. ; Inaba, M. ; Inoue, Y. ; Isenhower, D. ; Isenhower, L. ; Ishihara, M. ; Isobe, T. ; Issah, M. ; Isupov, Alexander ; Jacak, B.V. ; Jia, J. ; Jin, J. ; Jinnouchi, O. ; Johnson, B.M. ; Joo, K.S. ; Jouan, D. ; Kajihara, F. ; Kametani, S. ; Kamihara, N. ; Kamin, J. ; Kaneta, M. ; Kang, J.H. ; Kanou, H. ; Kawagishi, T. ; Kawall, D. ; Kazantsev, A.V. ; Kelly, S. ; Khanzadeev, A. ; Kikuchi, J. ; Kim, D.H. ; Kim, D.J. ; Kim, E. ; Kim, Y.-S. ; 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, P.J. ; Kubart, J. ; Kunde, G.J. ; Kurihara, N. ; Kurita, K. ; Kweon, M.J. ; Kwon, Y. ; Kyle, G.S. ; Lacey, R. ; Lai, Y.-S. ; Lajoie, J.G. ; Lebedev, A. ; Le Bornec, Y. ; Leckey, S. ; Lee, D.M. ; Lee, M.K. ; Lee, T. ; Leitch, M.J. ; Leite, M.A.L. ; Lenzi, B. ; Lim, H. ; Livs, T. ; Litvinenko, A. ; Liu, M.X. ; Li, X. ; Li, X.H. ; Love, B. ; Lynch, D. ; Maguire, C.F. ; Makdisi, Y.I. ; Malakhov, A. ; Malik, M.D. ; Manko, V.I. ; Mao, Y. ; Mavs, L. ; Masui, H. ; Matathias, F. ; McCain, M.C. ; McCumber, M. ; McGaughey, P.L. ; Miake, Y. ; Mikevs, P. ; Miki, K. ; Miller, T.E. ; Milov, A. ; Mioduszewski, S. ; Mishra, G.C. ; Mishra, M. ; Mitchell, J.T. ; Mitrovski, M. ; Morreale, A. ; Morrison, D.P. ; Moss, J.M. ; Moukhanova, T.V. ; Mukhopadhyay, D. ; Murata, J. ; Nagamiya, S. ; Nagata, Y. ; Nagle, J.L. ; Naglis, M. ; Nakagawa, I. ; Nakamiya, Y. ; Nakamura, T. ; Nakano, K. ; Newby, J. ; Nguyen, M. ; Norman, B.E. ; Nouicer, R. ; Nyanin, A.S. ; Nystrand, J. ; O'Brien, E. ; Oda, S.X. ; Ogilvie, C.A. ; Ohnishi, H. ; Ojha, I.D. ; Okada, H. ; Okada, K. ; Oka, M. ; Omiwade, O.O. ; Oskarsson, A. ; Otterlund, I. ; Ouchida, M. ; Ozawa, K. ; Pak, R. ; 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Staley, F. ; Stankus, P.W. ; Stenlund, E. ; Stepanov, M. ; Ster, A. ; Stoll, S.P. ; Sugitate, T. ; Suire, C. ; Sullivan, J.P. ; Sziklai, J. ; Tabaru, T. ; Takagi, S. ; Takagui, E.M. ; Taketani, A. ; Tanaka, K.H. ; Tanaka, Y. ; Tanida, K. ; Tannenbaum, M.J. ; Taranenko, A. ; Tarja, P. ; Thomas, T.L. ; Togawa, M. ; Toia, A. ; Tojo, J. ; Tomavs, L. ; Torii, H. ; Towell, R.S. ; Tram, V-N. ; Tserruya, I. ; Tsuchimoto, Y. ; Tuli, S.K. ; Tydesjo, H. ; Tyurin, N. ; Vale, C. ; Valle, H. ; van Hecke, H.W. ; Velkovska, J. ; Vertesi, R. ; Vinogradov, A.A. ; Virius, M. ; Vrba, V. ; Vznuzdaev, E. ; Wagner, M. ; Walker, D. ; Wang, X.R. ; Watanabe, Y. ; Wessels, J. ; White, S.N. ; Willis, N. ; Winter, D. ; Woody, C.L. ; Wysocki, M. ; Xie, W. ; Yamaguchi, Y.L. ; Yanovich, A. ; Yasin, Z. ; Ying, J. ; Yokkaichi, S. ; Young, G.R. ; Younus, I. ; Yushmanov, I.E. ; Zajc, W.A. ; Zaudtke, O. ; Zhang, C. ; Zhou, S. ; Zima, J. ; Zolin, L.

Published in: Phys.Rev.
Year: 2010
Vol.: C81
Page No: 034911
Pages: 56

Abstract: PHENIX has measured the e^+e^- pair continuum in sqrt(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^bar-c production, though 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 ~=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 ~=100 MeV. Theoretical models under predict the low mass, low p_T enhancement.

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