Determination of the longitudinal structure function at HERA from radiative events

Abstract

In deep-inelastic electron proton scattering, the emission of photons collinear with the incident electrons leads to a reduction of the effective beam energy. It is argued that this effect can be used to measure the longitudinal structure function at HERA. For an integrated luminosity of 200pb⁻¹, the statistical accuracy onR is in the range of ΔR≌0.05–0.25 for 6·10⁻⁴≤x≤2·10⁻² and 15GeV²≤Q ²≤120GeV². Systematic effects from photon identification and from the background of elasticep scattering in the luminosity monitor, as well as corrections from bin size effects and from cutting out lowp _T events are discussed.