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Low-momentum direct-photon measurement in Cu + Cu collisions at √sNN = 200 GeV
Physical Review C
  • A. Adare, University of Colorado, Boulder
  • Nathan C. Grau, Iowa State University and Augustana University
  • John C. Hill, Iowa State University
  • Nels J. Hotvedt, Iowa State University
  • John G. Lajoie, Iowa State University
  • Alexandre Lebedev, Iowa State University
  • S. H. Lee, Iowa State University
  • Craig Ogilvie, Iowa State University
  • Milap R. Patel, Iowa State University
  • H. Pei, Iowa State University
  • Timothy T. Rinn, Iowa State University
  • Marzia Rosati, Iowa State University
  • Jonathan C. Runchey, Iowa State University
  • M. Shimomura, Iowa State University and University of Tsukuba
  • S. Skutnik, Iowa State University
  • Carla Vale, Iowa State University
  • Feng Wei, Iowa State University and New Mexico State University
  • et al.
  • PHENIX Collaboration, PHENIX Collaboration
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Published Version
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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.


This article is published as Adare, A., S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander et al. "Low-momentum direct-photon measurement in Cu+ Cu collisions at s N N= 200 GeV." Physical Review C 98, no. 5 (2018): 054902. DOI: 10.1103/PhysRevC.98.054902. Posted with permission.

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Creative Commons Attribution 4.0
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American Physical Society
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Citation Information
A. Adare, Nathan C. Grau, John C. Hill, Nels J. Hotvedt, et al.. "Low-momentum direct-photon measurement in Cu + Cu collisions at √sNN = 200 GeV" Physical Review C Vol. 98 Iss. 5 (2018) p. 054902
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