Hard QED radiation at HERA

Abstract

The deep-inelastic electron-proton collisions at HERA are frequently associated with emission of hard photons. A large fraction of these events can be identified either by the direct detection of radiative photons or, indirectly, by a mismatch between the event kinematics determined from the scattered electron energy and its angle and that determined from the hadronic flow associated with a deep-inelastic scattering. This unique feature of HERA experiments provides an experimental check on the size of radiative corrections. The emission of photons collinear with the incident electrons leads to a reduction of the effective beam energy. This effect can be used to measure the longitudinal structure function.