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Centrality dependence of low-momentum direct-photon production in Au + Au collisions at $$sqrt{s_{NN}} = 200$$ GeV

$$sqrt{s_{NN}}$$=200GeVでの金-金衝突における低運動量直接光子生成のcentrality依存性

Adare, A.*; 今井 憲一; 谷田 聖; PHENIX Collaboration*; 他477名*

Adare, A.*; Imai, Kenichi; Tanida, Kiyoshi; PHENIX Collaboration*; 477 of others*

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at $$sqrt{s_{NN}} = 200$$ GeV down to $$p_T < 0.4 ;{rm GeV}/c$$. 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 $$p_T$$. We find an excess of direct photons above the $$N_{rm coll}$$-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 $$p_T$$ range 0.6-2.0 GeV/$$c$$. While the shape of the $$p_T$$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $$N_{rm part}^{alpha}$$, where $$alpha = 1.38 pm 0.03({rm stat}) pm 0.07({rm syst})$$.

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パーセンタイル:0.68

分野:Physics, Nuclear

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