Detailed measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi>e</mml:mi><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>pair continuum in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>p</mml:mi><mml:mo>+</mml:mo><mml:mi>p</mml:mi></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Au</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">Au</mml:mi></mml:mrow></mml:math>collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:mrow><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi mathvariant="italic">NN</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:msqrt><mml:mo>=</mml:mo><mml:mn>200</mml:mn></mml:mrow></mml:math>GeV and implications for direct photon production
A. AdareUniversity of Colorado, Boulder, Colorado 80309, USAS. AfanasievJoint Institute for Nuclear Research, RU-141980 Dubna, Moscow Region, RussiaC. AidalaColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAN. N. AjitanandChemistry Department, Stony Brook University, Stony Brook, SUNY, New York 11794-3400, USAY. AkibaRIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USAH. Al-BatainehNew Mexico State University, Las Cruces, New Mexico 88003, USAJ. AlexanderChemistry Department, Stony Brook University, Stony Brook, SUNY, New York 11794-3400, USAA. Al-JamelNew Mexico State University, Las Cruces, New Mexico 88003, USAK. AokiKyoto University, Kyoto 606-8502, JapanL. AphecetcheSUBATECH (Ecole des Mines de Nantes, CNRS-IN2P3, Université de Nantes) BP 20722-44307, Nantes, FranceR. ArméndarizNew Mexico State University, Las Cruces, New Mexico 88003, USAS. H. AronsonBrookhaven National Laboratory, Upton, New York 11973-5000, USAJ. AsaiRIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USAE. T. AtomssaLaboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, FranceR. AverbeckDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAT. C. AwesOak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USAB. AzmounBrookhaven National Laboratory, Upton, New York 11973-5000, USAV. BabintsevIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaG. BaksayFlorida Institute of Technology, Melbourne, Florida 32901, USAL. BaksayFlorida Institute of Technology, Melbourne, Florida 32901, USAA. BaldisseriDapnia, CEA Saclay, F-91191, Gif-sur-Yvette, FranceK. N. BarishUniversity of California-Riverside, Riverside, California 92521, USAP. D. BarnesLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USAB. BassalleckUniversity of New Mexico, Albuquerque, New Mexico 87131, USAS. BatheUniversity of California-Riverside, Riverside, California 92521, USAS. BatsouliColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAV. BaublisPNPI, Petersburg Nuclear Physics Institute, Gatchina, Leningrad region, RU-188300, RussiaF. BauerUniversity of California-Riverside, Riverside, California 92521, USAA. BazilevskyBrookhaven National Laboratory, Upton, New York 11973-5000, USAS. BelikovBrookhaven National Laboratory, Upton, New York 11973-5000, USAR. BennettDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAY. BerdnikovSaint Petersburg State Polytechnic University, St. Petersburg, RussiaA. A. BickleyUniversity of Colorado, Boulder, Colorado 80309, USAM. T. BjorndalColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAJ. G. BoissevainLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USAH. BorelDapnia, CEA Saclay, F-91191, Gif-sur-Yvette, FranceK. BoyleDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAM. L. BrooksLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USAD. S. BrownNew Mexico State University, Las Cruces, New Mexico 88003, USAD. BucherInstitut für Kernphysik, University of Muenster, D-48149 Muenster, GermanyH. BueschingBrookhaven National Laboratory, Upton, New York 11973-5000, USAV. BumazhnovIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaG. BunceBrookhaven National Laboratory, Upton, New York 11973-5000, USAJ. M. Burward-HoyLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USAS. ButsykDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAS. CampbellDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAJ.-S. ChaiKAERI, Cyclotron Application Laboratory, Seoul, KoreaB. S. ChangYonsei University, IPAP, Seoul 120-749, KoreaJ. L. CharvetDapnia, CEA Saclay, F-91191, Gif-sur-Yvette, FranceS. ChernichenkoIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaJ. ChibaKEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, JapanC. Y.Columbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAM. ChiuColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAI. J. ChoiYonsei University, IPAP, Seoul 120-749, KoreaT. ChujoVanderbilt University, Nashville, Tennessee 37235, USAP. ChungChemistry Department, Stony Brook University, Stony Brook, SUNY, New York 11794-3400, USAA. ChurynIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaV. CiancioloOak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USAC. R. ClevenGeorgia State University, Atlanta, Georgia 30303, USAY. CobigoDapnia, CEA Saclay, F-91191, Gif-sur-Yvette, FranceB. ColeColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAM. P. CometsIPN-Orsay, Université Paris Sud, CNRS-IN2P3, BP1, F-91406, Orsay, FranceP. ConstantinIowa State University, Ames, Iowa 50011, USAM. CsanádELTE, Eötvös Loránd University, H-1117 Budapest, Pázmány P. s. 1/A, HungaryT. CsörgőKFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences (MTA KFKI RMKI), H-1525 Budapest 114, PO Box 49, Budapest, HungaryT. DahmsDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAK. DasFlorida State University, Tallahassee, Florida 32306, USAG. DavidBrookhaven National Laboratory, Upton, New York 11973-5000, USAM. B. DeatonAbilene Christian University, Abilene, Texas 79699, USAK. DehmeltFlorida Institute of Technology, Melbourne, Florida 32901, USAH. DelagrangeSUBATECH (Ecole des Mines de Nantes, CNRS-IN2P3, Université de Nantes) BP 20722-44307, Nantes, FranceA. DenisovIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaD. d’EnterriaColumbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USAA. DeshpandeDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAE. J. DesmondBrookhaven National Laboratory, Upton, New York 11973-5000, USAO. DietzschUniversidade de São Paulo, Instituto de Física, Caixa Postal 66318, São Paulo CEP05315-970, BrazilA. DionDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAM. DonadelliUniversidade de São Paulo, Instituto de Física, Caixa Postal 66318, São Paulo CEP05315-970, BrazilJ. L. DrachenbergAbilene Christian University, Abilene, Texas 79699, USAO. DrapierLaboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, FranceA. DreesDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAA. K. DubeyWeizmann Institute, Rehovot 76100, IsraelA. DurumIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, RU-142281, RussiaV. DzhordzhadzeUniversity of California-Riverside, Riverside, California 92521, USAY. V. EfremenkoOak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USAJ. EgdemirDepartment of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794, USAF. EllinghausUniversity of Colorado, Boulder, Colorado 80309, USAW. S. EmamUniversity of California-Riverside, Riverside, California 92521, USAA. EnokizonoHiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, JapanH. En’yoRIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USAB. EspagnonIPN-Orsay, Université Paris Sud, CNRS-IN2P3, BP1, F-91406, Orsay, FranceS. EsumiInstitute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305, JapanO. EyserUniversity of California-Riverside, Riverside, California 92521, USAD. E. FieldsRIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USAM. FingerCharles University, Ovocný trh 5, Praha 1, 116 36, Prague, Czech RepublicF. FleuretLaboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, FranceS. FokinRussian Research Center “Kurchatov Institute,” Moscow, RussiaB. ForestierLPC, Université Blaise Pascal, CNRS-IN2P3, Clermont-Fd, 63177 Aubiere Cedex, FranceZ. FraenkelWeizmann Institute, Rehovot 76100, Israel
2010lv
ABI
Аннотация
PHENIX has measured the ${e}^{+}{e}^{\ensuremath{-}}$ pair continuum in $\sqrt{{s}_{\mathit{NN}}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions over a wide range of mass and transverse momenta. The ${e}^{+}{e}^{\ensuremath{-}}$ yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the $\ensuremath{\phi}$ and the $J/\ensuremath{\psi}$ meson, the yield is consistent with expectations from correlated $c\mathrm{c\ifmmode \bar{}\else \={}\fi{}}$ production, although other mechanisms are not ruled out. In the low-mass region, below the $\ensuremath{\phi}$, the $p+p$ inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the $\mathrm{Au}+\mathrm{Au}$ minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of $4.7\ifmmode\pm\else\textpm\fi{}{0.4}^{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.5}^{\mathrm{syst}}\ifmmode\pm\else\textpm\fi{}{0.9}^{\mathrm{model}}$. At low mass (${m}_{\mathit{ee}}<0.3$ GeV/${c}^{2}$) and high ${p}_{T}$ ($1<{p}_{T}<5$ GeV/$c$) an enhanced ${e}^{+}{e}^{\ensuremath{-}}$ 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 $\mathrm{Au}+\mathrm{Au}$ collisions, the excess of the direct photon yield over the $p+p$ is exponential in ${p}_{T}$, with inverse slope $T=221\ifmmode\pm\else\textpm\fi{}{19}^{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{19}^{\mathrm{syst}}$ MeV. Hydrodynamical models with initial temperatures ranging from ${T}_{\mathrm{init}}\ensuremath{\simeq}300--600$ MeV at times of $0.6--0.15$ fm/$c$ after the collision are in qualitative agreement with the direct photon data in $\mathrm{Au}+\mathrm{Au}$. 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 $T\ensuremath{\simeq}100$ MeV. Theoretical models underpredict the low-mass, low-${p}_{T}$ enhancement.
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