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

Abstract

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 $d{N}_{\mathrm{ch}}/d\eta$ observed in Au$+$Au at the same collision energy.

arXiv comment453 authors from 74 institutions, 12 pages, 8 figures, 2 tables. v3 is version accepted for publication in Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

References in corpus (18)

• PYTHIA 6.4 Physics and Manual
• PYTHIA 6.2 Physics and Manual
• A Brief Introduction to PYTHIA 8.1
• Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
• Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
• Global QCD Analysis of Parton Structure of the Nucleon: CTEQ5 Parton Distributions
• Enhanced production of direct photons in Au+Au collisions at sqrt(s_NN)=200 GeV and implications for the initial temperature
• Hadronic Production of Thermal Photons
• Detailed measurement of the e+e- pair continuum in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV and implications for direct photon production
• Direct photon production in Pb-Pb collisions at $\sqrt{s_\rm{NN}}$ = 2.76 TeV
• Common Suppression Pattern of eta and pi^0 Mesons at High Transverse Momentum in Au+Au Collisions at sqrt(s_NN) = 200 GeV
• Quantitative Constraints on the Transport Properties of Hot Partonic Matter from Semi-Inclusive Single High Transverse Momentum Pion Suppression in Au+Au collisions at sqrt(s_NN) = 200 GeV
• Transverse energy production and charged-particle multiplicity at midrapidity in various systems from $\sqrt{s_{NN}}=7.7$ to 200 GeV
• Energy dependence of pi-zero production in Cu+Cu collisions at sqrt(s_NN) = 22.4, 62.4, and 200 GeV
• Direct photon production in d+Au collisions at sqrt(s_NN)=200 GeV
• Electromagnetic Probes at RHIC-II
• System-size dependence of open-heavy-flavor production in nucleus-nucleus collisions at $\sqrt{s_{{}_{NN}}}$=200 GeV
• Measurements of $e^{+}{e}^{-}$ pairs from open heavy flavor in $p$+$p$ and $d$+$A$ collisions at $\sqrt{s_{NN}}=200$ GeV

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