Thermal photons and collective flow at energies available at the BNL Relativistic Heavy-Ion Collider

Hendrik van Hees, Charles Gale, and Ralf Rapp
Phys. Rev. C 84, 054906 – Published 9 November 2011

Abstract

We update our calculations of thermal-photon production in nuclear collisions at the BNL Relativistic Heavy-Ion Collider (RHIC). Specifically, we address the recent experimental observation of an elliptic flow of direct photons comparable in magnitude to that of pions, which is at variance with expectations based on quark-gluon plasma (QGP) dominated photon radiation. Our thermal emission rate is based on previous work, i.e., resummed leading-order QGP emission and in-medium hadronic rates in the confined phase. These rates are nearly degenerate at temperatures close to the expected QCD-phase change. The rates are convoluted over an improved elliptic-fireball expansion with transverse- and elliptic-flow fields quantitatively constrained by empirical light- and strange-hadron spectra. The resulting direct-photon spectra in central Au-Au collisions are characterized by hadron-dominated emission up to transverse momenta of 23GeV. The associated large elliptic flow in the hadronic phase mitigates the discrepancy with the measured photon-v2 compared to scenarios with QGP-dominated emission.

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  • Received 10 August 2011

DOI:https://doi.org/10.1103/PhysRevC.84.054906

©2011 American Physical Society

Authors & Affiliations

Hendrik van Hees

  • Institut für Theoretische Physik, Goethe-Universität Frankfurt, Germany, and Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Str. 1, D-60438 Frankfurt, Germany

Charles Gale

  • Department of Physics, McGill University, 3600 University Street, Montreal, Canada H3A 2T8

Ralf Rapp

  • Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-3366, USA

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Issue

Vol. 84, Iss. 5 — November 2011

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