Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{ s_\mathrm{ NN}} = 17.4\mathrm{ GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{ T}$ are derived and compared to the results for Pb+Pb collisions at $\sqrt{ s_\mathrm{ NN}} = 17.3$ GeV. The production of the $\eta$ meson, which is an important input to the direct photon signal extraction, has been determined in the $\eta \rightarrow 2\gamma$ channel for p+C collisions at $\sqrt{ s_\mathrm{ NN}} = 17.4\mathrm{ GeV}$.
Categories: nucl-ex