Volume 345 - International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (HardProbes2018) - Electroweak Probes
PHENIX measurements of beam energy and centrality dependence of direct photon emission in heavy ion collisions
A. Drees
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Pre-published on: 2019 January 21
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Abstract
In this talk the PHENIX collaboration presents new measurements of low momentum direct photons from Cu+Cu at 200 GeV and Au+Au at 62.4 GeV and 39 GeV. A large excess of direct photons over the scaled $p$+$p$ yield is found. The comparison of the new data with data from Au+Au at 200 GeV and ALICE data from 2.76 TeV reveals that at low-$p_{T}$ the spectra of direct photons and their integrated yield above 1 GeV/c follow a universal scaling as a function of the charged-particle multiplicity, $(dN_{ch}/d\eta)^{\alpha}$, with $\alpha = 1.25$, independent of collision centrality or center of mass energy. The observed scaling properties suggests that the emission source has similar properties for all observed systems.
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