Abstract
The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from collisions at down to . Photons are detected via photon conversions to pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low . We find an excess of direct photons above the -scaled yield measured in collisions. This excess yield is well described by an exponential distribution with an inverse slope of about in the range . While the shape of the distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with , where .
3 More- Received 23 May 2014
- Revised 16 March 2015
DOI:https://doi.org/10.1103/PhysRevC.91.064904
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