Low Q^2 jet production at HERA in next-to-leading order QCD

We present next-to-leading order calculations of one- and two-jet production in eP collisions at HERA for photon virtualities in the range GeV. Soft and collinear singularities are extracted using the phase space slicing method. Numerical results are presented for HERA conditions with the Snowmass jet definition. The transition between photoproduction and deep-inelastic scattering is investigated in detail. We compare two approaches, the usual deep-inelastic theory, where the virtual photon couples only directly to quarks and antiquarks, and the photoproduction approach, where the photon couples either in the direct way or in the resolved way via the parton constituents of the virtual photon with the proton constituents. Finally we compare with recent H1 data of the dijet rate obtained for various photon virtualities with special attention to the region, in which two jets have equal transverse momenta. Received: 23 April 1998 / Published online: 26 August 1998