Nonprompt direct-photon production in Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

Abstract

The measurement of the direct-photon spectrum from Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV is presented by the PHENIX collaboration using the external-photon-conversion technique for 0\%--93\% central collisions in a transverse-momentum ($p_T$) range of 0.8--10 GeV/$c$. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for $p_T<6$ GeV/$c$. Nonprompt direct photons are measured by subtracting the prompt component, which is estimated as $N_{\mathrm{coll}}$-scaled direct photons from $p$$+$$p$ collisions at 200 GeV, from the direct-photon spectrum. Results are obtained for $0.8<p_T<6.0$ GeV/$c$ and suggest that the spectrum has an increasing inverse slope from $\approx 0.2$ to 0.4 GeV/$c$ with increasing $p_T$, which indicates a possible sensitivity of the measurement to photons from earlier stages of the evolution of the collision. In addition, like the direct-photon production, the $p_T$-integrated nonprompt direct-photon yields also follow a power-law scaling behavior as a function of collision-system size. The exponent, $\alpha$, for the nonprompt component is found to be consistent with 1.1 with no apparent $p_T$ dependence.

336 authors from 71 institutions, 26 pages, 30 figures, 4 tabels, 2014 data. v2 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 (6)

• Measurement of direct photon production in p + p collisions at sqrt(s) = 200 GeV
• Pseudo-Critical Enhancement of Thermal Photons in Relativistic Heavy-Ion Collisions
• Multi-messenger heavy-ion collision physics
• The Glasma, Photons and the Implications of Anisotropy
• Universal Parametrization of Thermal Photon Rates in Hadronic Matter
• The Magneto-Sono-Luminescence and its signatures in photon and dilepton production in heavy ion collisions

Cited by in corpus (4)

• Measurement of the inclusive isolated-photon production cross section in pp and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV
• Rotating synchrotron radiation: Photon emission from magnetized and rotating quark-gluon plasma
• Photon emission from weakly magnetized neutral pions
• A background for thermal photons in heavy ion collisions