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Low-momentum direct-photon measurement in Cu plus Cu collisions at root S-NN=200 GeV

Author
Adare A. University of Colorado, USA
Finger Miroslav, prof. Ing. DrSc. Faculty of Mathematics and Physics, Charles University in Prague
Finger Michael, M.Sc. CSc. Faculty of Mathematics and Physics, Charles University in Prague, JINR Dubna
Slunečka Miloš, Ing. Faculty of Mathematics and Physics, Charles University in Prague, JINR Dubna
et al.  PHENIX collaboration

Year
2018

Scientific journal
Physical Review C, 98 (5), 054902

Web


Abstract
We 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 root S-NN = 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 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 +/- 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 dN(ch)/d eta observed in Au+Au at the same collision energy.

Cite article as:
A. Adare, M. Finger, M. Finger, M. Slunečka, . et al., "Low-momentum direct-photon measurement in Cu plus Cu collisions at root S-NN=200 GeV", Physical Review C, 98 (5), 054902 (2018)