Photon and Neutral π<sup>0</sup production in <sup>197</sup>Au + <sup>197</sup>Au collisions at √s<sub>NN</sub> = 130 GeV

Abstract

Inclusive transverse momentum spectra of photons and {pi}{sup 0}s at mid-rapidity are studied as a function of collision centrality for {sup 197}Au+ {sup 197}Au collisions at {radical}s{sub NN} = 130 GeV. Photon pair conversions have been reconstructed from charged tracks measured by the main Time Project Chamber of the STAR experiment at the RHIC heavy ion facility. The transverse momentum resolution of photons with this method is estimated to be {Delta}p{sub t}/p{sub t} = 2% at 0.125 GeV/c and 5% at 2.5 GeV/c. Photon spectra were measured up to a transverse momentum of 2.4 GeV/c between {+-} 0.5 units of rapidity. The dominant photon production mechanism, the {pi}{sup 0} {yields} {gamma}{gamma} decay, was measured between 0.25-2.5 GeV/c and {+-} 1 units of rapidity. Spectra are reported for the top 11%, 11-34% and 34-85% centrality classes. It was observed that in mid-central and central collisions the relative contribution of the {pi}{sup 0} {yields} {gamma}{gamma} decay to the inclusive photon spectrum decreases above a transverse momentum of 1.65 GeV/c. In central collisions the magnitude of the decrease from p{sub t} = 1.65 GeV/c to 2.4 GeV/c is 20%. It is unlikely that contributions from other {pi}{sup 0} decay channels and other particlemore » decays fully explain this decrease. The centrality dependence on the shapes of the {pi}{sup 0} spectra was analyzed with Boltmann and Bose-Einstein functions. In the transverse momentum windows of the spectra, the extracted temperatures are near 0.295 GeV. These temperatures are substantially higher than those extracted from {pi}{sup {+-}} spectra in a lower range of transverse momentum. This is an indication that the shapes of the pion spectra deviate from purely exponential shapes.« less