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Low-momentum direct-photon measurement in Cu + Cu collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

$$sqrt{s_{_{NN}}}=200$$GeVの銅+銅衝突における低運動量直接光子の測定

Adare, A.*; 長谷川 勝一; 今井 憲一; 永宮 正治; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他448名*

Adare, A.*; Hasegawa, Shoichi; Imai, Kenichi; Nagamiya, Shoji; Sako, Hiroyuki; Sato, Susumu; Tanida, Kiyoshi; PHENIX Collaboration*; 448 of others*

We have measured direct photons for $$p_T< 5~$$GeV/$$c$$ in minimum bias and 0% - 40% most central events at midrapidity for Cu$$+$$Cu collisions at $$sqrt{s_{_{NN}}}=200$$ GeV. The $$e^{+}e^{-}$$ contribution from quasi-real direct virtual photons has been determined as an excess over the known hadronic contributions in the $$e^{+}e^{-}$$ mass distribution. A clear enhancement of photons over the binary scaled $$p$$$$+$$$$p$$ fit is observed for $$p_T < 4$$ GeV/$$c$$ in Cu$$+$$Cu data. The $$p_T$$ spectra are consistent with the Au$$+$$Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the $$p$$$$+$$$$p$$ baseline are 285$$pm$$53(stat)$$pm$$57(syst)~MeV/$$c$$ and 333$$pm$$72(stat)$$pm$$45(syst)~MeV/$$c$$ for minimum bias and 0% - 40% most central events, respectively. The rapidity density, $$dN/dy$$, of photons demonstrates the same power law as a function of $$dN_{rm ch}/deta$$ observed in Au$$+$$Au at the same collision energy.

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パーセンタイル:100

分野:Physics, Nuclear

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