Direct photons have been measured in $\sqrt{s_{{}_{NN}}}=200$ GeV $d+\text{Au}$ collisions at midrapidity. A wide $p_T$ range is covered by measurements of nearly real virtual photons ($1<p_T<6$ GeV/$c$) and real photons ($5<p_T<16$ GeV/$c$). The invariant yield of the direct photons in $d+\text{Au}$ collisions over the scaled $p+p$ cross section is consistent with unity. Theoretical calculations assuming standard cold-nuclear-matter effects describe the data well for the entire $p_T$ range. This indicates that the large enhancement of direct photons observed in $\mathrm{Au}+\mathrm{Au}$ collisions for $1.0<p_T<2.5$ GeV/$c$ is attributable to a source other than the initial-state nuclear effects.

• Received 6 August 2012

DOI:https://doi.org/10.1103/PhysRevC.87.054907