Abstract
The production of photons at large transverse momentum can be used as a direct probe of quark and gluon subprocesses at short distances. We calculate the cross section for high-${p}_{T}$ photons produced in $\mathrm{pp}$ collisions from lowest-order quantum-chromodynamics (QCD) and higher-order constituent-interchange-model (CIM) processes. We find that CIM terms dominate both $\ensuremath{\gamma}$ and $\ensuremath{\pi}$ spectra until very high ${p}_{T}$-although there are regions of $s$ and ${p}_{T}$ where the CIM contributions dominate the $\ensuremath{\gamma}$ spectrum but the $\ensuremath{\pi}$ spectrum already shows the scaling behavior of lowest-order QCD, and also vice versa. We emphasize that in some processes (e.g., gluon + quark \ensuremath{\rightarrow} photon + quark), the photon is produced without accompanying toward-side hadrons.
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