Inclusive Production of Direct Photons in 200-GeV/cCollisions

Abstract

The authors have measured the inclusive production of direct photons in the transverse momentum ($p_T$) range 2.1-5.0 GeV/c in 200-GeV/c collisions of protons and ${\pi }^{+}$ mesons on a carbon target. A significant yield of direct photons was observed for $p_T>2.5\mathrm{}$ GeV/c. The invariant cross section for direct-photon production, when compared with measurements from the CERN intersecting storage rings, can be expressed in terms of $p_T$ and $x_T=2\mathrm{}{p}_T\sqrt{s} \mathrm{as} (42\mathrm{}\pm 14){(1-x_T)}^{8.1\pm 1.0}{p_T}^{-6.6\mathrm{}\pm 0.3}$ μb/${\mathrm{GeV}}^2$ for the c.m. energy range from $\sqrt{s}=19.4\mathrm{} \mathrm{to} 63$ GeV, and for the $x_T$ range from 0.2 to 0.5.