Parton distributions incorporating QED contributions.

Abstract

We perform a global parton analysis of deep inelastic and related hard-scattering data, including O( QED) corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e. up 6= dn, which is found to be unambiguously in the direction to reduce the NuTeV sin2 W anomaly. A second consequence is the appearance of photon parton distributions (x,Q2) of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes eN → e X; our predictions are in agreement with the present data.