Measurement of direct-photon production at the Fermilab Tevatron fixed target energies

Measurements of the production of high transverse momentum direct photons by a $515\mathrm{G}\mathrm{e}\mathrm{V}/c$ ${\pi }^{-}$ beam and 530 and $800\mathrm{G}\mathrm{e}\mathrm{V}/c$ proton beams in interactions with beryllium and hydrogen targets are presented. The data span the kinematic ranges of $3.5<p_T<12\mathrm{G}\mathrm{e}\mathrm{V}/c$ in transverse momentum and 1.5 units in rapidity. The inclusive direct-photon cross sections are compared with next-to-leading-order perturbative QCD calculations and expectations based on a phenomenological parton-$k_T$ model.