Direct Photoproduction of Jets in the KT Factorisation Prescription

Abstract

We study the cross section for dijet production via direct photons, as seen at the HERA collider. Rather than assuming the standard factorisation formula for the cross section (where the incoming partons are assumed to be on-shell), we use the $k_T$-factorisation formula. This formalism ought to be more appropriate for jet production in regions where the cross section is sensitive to the small-$x$ parton distribution functions. We study the rapidity distribution and the azimuthal angular distribution of the jets and compare with the traditional approach. Our calculations reveal a breakdown of the traditional approach as one moves into the regime of small $x$.