Low-momentum direct-photon measurement in Cu + Cu collisions at
Here, 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 = 200GeV. 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 < 4GeV/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.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Contributing Organization:
- PHENIX Collaboration
- Grant/Contract Number:
- SC0012704
- OSTI ID:
- 1482284
- Alternate ID(s):
- OSTI ID: 1482571
- Report Number(s):
- BNL-209456-2018-JAAM; PRVCAN; 054902
- Journal Information:
- Physical Review C, Journal Name: Physical Review C Vol. 98 Journal Issue: 5; ISSN 2469-9985
- Publisher:
- American Physical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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