Eur. Phys. J. C (2006) 46: 451-464
https://doi.org/10.1140/epjc/s2006-02504-0

Theoretical Physics

Probing the QCD equation of state with thermal photons in nucleus–nucleus collisions at RHIC

¹ Nevis Laboratories, Columbia University, Irvington, NY, 10533, USA
² RRC “Kurchatov Institute”, Kurchatov Sq. 1, Moscow, 123182, Russia

^* e-mail: denterria@nevis.columbia.edu

Received: 7 October 2005
Revised: 29 December 2005
Published online: 30 March 2006

Abstract

Thermal photon production at mid-rapidity in Au+Au reactions at is studied in the framework of a hydrodynamical model that describes efficiently the bulk identified hadron spectra at RHIC. The combined thermal plus NLO pQCD photon spectrum is in good agreement with the yields measured by the PHENIX experiment for all Au+Au centralities. Within our model, we demonstrate that the correlation of the thermal photon slopes with the charged hadron multiplicity in each centrality provides direct empirical information on the underlying degrees of freedom and on the form of the equation of state, s(T)/T³, of the strongly interacting matter produced in the course of the reaction.