Speaker
Description
PHENIX has made a comprehensive measurement of low p$_\mathrm{T}$ direct photon yield in Au+Au collisions at 200 GeV that show both a large yield and a large azimuthal anisotropy produced. The mechanism for such simultaneous large production is not well understood yet.
Recently the PHENIX collaboration has improved on those measurements by using the Au+Au data collected in 2014 which provides a 10-fold increase in statistics. Furthermore, PHENIX has found that the low p$_\mathrm{T}$ direct photon yield dN$_{\gamma}$/d$\eta$ is proportional to (dN$_\mathrm{ch}$/d$\eta$)$^\alpha$. This scaling holds for beam energies both at RHIC and at the LHC in large-on-large systems. An extrapolation to smaller systems suggests an onset of QGP formation at low dN$_\mathrm{ch}$/d$\eta$.
In this talk I will show the most recent results on direct photon measurements from large and small systems.
