Resolved virtual photons in the small $x$ domain

Abstract

It has been found that recent results on forward jet production from deep inelastic scattering can neither be reproduced by models which are based on leading order $α_s$ QCD matrix elements and parton showers nor by next-to-leading order calculations. The measurement of forward jet cross sections has been suggested as a promising probe of new small $\xbj$ parton dynamics and the question is whether these data provide an indication of this. The same question arises for other experimental data in deep inelastic scattering at small $\xbj$ which can not be described by conventional models for deep inelastic scattering. In this paper the influence of resolved photon processes has been investigated and it has been studied to what extent the inclusion of such processes in addition to normal deep inelastic scattering leads to agreement with data. It is shown that two DGLAP evolution chains from the hard scattering process towards the proton and the photon, respectively, are sufficient to describe effects, observed in the HERA data, which have been attributed to BFKL dynamics.