Download or read book Centrality Dependence of Low-momentum Direct-photon Production in [math][mrow][mi]Au[/mi][mo]+[/mo][mi]Au[/mi][/mrow][/math] Collisions at [math][mrow][msqrt][msub][mi][/mi][mrow][mi Mathvariant written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at √sNN = 200 GeV down to pT = 0.4 GeV/c. Photons are detected via photon conversions to e+e− pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT . In this paper, we find an excess of direct photons above the Ncoll-scaled yield measured in p+p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/c in the pT range from 0.6-2.0 GeV/c. Finally, in this study, while the shape of the pT distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with N [alpha] part, where [alpha] = 1.38±0.03(stat)±0.07(syst).