Diffractive hard scattering

We discuss high energy hadron collisions that contain a hard scattering, in the sense that a W, a Z, very heavy quarks, or high pT jets are produced, yet are diffractive, in the sense that one of the incident hadrons is scattered with only a small energy loss. In our approach, the cross section for such diffractive hard scattering is a part of the normal hard scattering inclusive cross section, as calculated using perturbative quantum chromodynamics. We use Regge phenomenology in combination with perturbative QCD to estimate that a substantial fraction (perhaps 30%) of all hard scattering events are diffractive. Measurement of diffractive hard scattering cross sections would illuminate the short distance gluon and quark content of the pomeron, which has been found to play a fundamental role in forward hadron scattering. (orig.)