Scale-violation effects in large-pTdirect photon production

The contribution of the quantum-chromodynamic (QCD) perturbation diagrams $q+g\to \gamma +q$ and $q+\overline{q}\to \gamma +g$ (where $q$,$g$,$\overline{q}$ denote quark, gluon, antiquark) to large-$p_T$ direct $\gamma$ production is studied in detail. It is shown that inclusion of QCD scale violations in the $q$, $g$, and $\overline{q}$ distributions reduces the predicted yield for $p+p\to \gamma +X$ by one order of magnitude. At $\sqrt{s}=53\mathrm{}$ GeV and $p_T\simeq 10$ GeV, with the experimental inclusive cross section $E \frac{d\sigma (p+p\to {\pi }^0+X)}{d^{3}p}\sim {10}^{-36\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{GeV}}^{-2\mathrm{}}$, the contribution of these diagrams if found to give a ratio of $\gamma$ to ${\pi }^0$ of 5-15%.