Seminar in Hadronic Physics

Experimental results of thermal photon production in heavy ion collisions

Wenqing Fan

Stony Brook University

Direct photons are unique probes to study the thermal properties of Quark Gluon Plasma (QGP) and the dynamic evolution of the ultra-relativistic heavy ion collision system. The produced photons do not interact with the medium strongly, hence carrying direct information of their creation point. Low transverse momentum (p_T) direct photons are believed to originate primarily from thermal radiation of the QGP and hadronic gas (HG) phase; however, calculations of thermal photon emission fall short in describing the measured direct photon yield and the anisotropy at the same time. The question is tied to the photon production mechanism in heavy ion collisions, whether the production rates of the known photon-emitting sources need to be modified or there are some other sources that need to be included in the current theoretical picture. To provide more insight into this question, many collision systems have been explored both at RHIC and LHC. In this talk, I will discuss the scaling behavior of the direct photon production as a function of system size. I will also present a more precise study of the p_T and multiplicity dependence of the direct photon production using the high statistics dataset of Au+Au collisions at 200 GeV collected by the PHENIX experiment at RHIC in 2014.