Production of real photons at large transverse momentum inppcollisions

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 $\gamma$ and $\pi$ spectra until very high $p_T$-although there are regions of $s$ and $p_T$ where the CIM contributions dominate the $\gamma$ spectrum but the $\pi$ spectrum already shows the scaling behavior of lowest-order QCD, and also vice versa. We emphasize that in some processes (e.g., gluon + quark → photon + quark), the photon is produced without accompanying toward-side hadrons.