The production of high-$p_T$ direct photons is studied using quantum chromodynamics. The theoretical predictions are shown to be compatible with the existing data over the energy interval $20<\mathrm{}\sqrt{s}<63\mathrm{}$ GeV. In addition, the possibility of using a high-$p_T$ direct-photon trigger in hadronic-jet experiments is studied. By simultaneously triggering on a direct photon and on the away-side hadronic jet it is possible to obtain more precise information concerning the underlying dynamical subprocesses than if a two-jet trigger is used. In particular, one can, by using a combination of ${\pi }^{\pm }$, $p$, and $\overline{p}$ beams, measure both the pion quark and gluon distribution functions as well as the gluon distribution function for the proton. Furthermore, if particle identification is available for the away-side jet, one can separately measure various quark and gluon fragmentation functions. A method of measuring the $Q^2$ dependences of these various functions is also discussed.

• Received 10 March 1980

DOI:https://doi.org/10.1103/PhysRevD.22.1609