Physics and Astronomy
Journal or Book Title
Physical Review C
We measured direct photons for pT<5GeV/c in minimum bias and 0%–40% most-central events at midrapidity for Cu+Cu collisions at √sNN=200 GeV. The e+e− contribution from quasireal 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 pT<4 GeV/c in Cu+Cu data. The pT 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±53(stat)±57(syst)MeV/c and 333±72(stat)±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 dNch/dη observed in Au+Au at the same collision energy.
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American Physical Society
Adare, A.; Grau, Nathan C.; Hill, John C.; Hotvedt, Nels J.; Lajoie, John G.; Lebedev, Alexandre; Lee, S. H.; Ogilvie, Craig; Patel, Milap R.; Pei, H.; Rinn, Timothy T.; Rosati, Marzia; Runchey, Jonathan C.; Shimomura, M.; Skutnik, S.; Vale, Carla; Wei, Feng; et al.; and PHENIX Collaboration, "Low-momentum direct-photon measurement in Cu + Cu collisions at √sNN = 200 GeV" (2018). Physics and Astronomy Publications. 501.