Jet Production at HERA

I review the status of perturbative QCD calculations for jet production in eP-scattering at HERA. I will discuss possibilities of combining fixed order, especially higher order, calculations and parton showers.Comment: 13 pages, 5 eps figure

Forward Jet Production at HERA

We discuss forward jet production data recently published by the H1 and ZEUS collaborations at HERA. We review how several Monte-Carlo models compare to the data. QCD calculations based on the BFKL formalism and on fixed NLO perturbation theory with and without resolved virtual photons are described.Comment: 10 pages, 4 eps figures; talk given at the Ringberg Workshop 'New Trends in HERA Physics 1999

Probing the parton densities of virtual photons with the reaction gamma^*gamma->jets at LEP

We present a next-to-leading order calculation of jet production in gamma^*gamma collisions from e+e- scattering in a region where the virtuality Q^2 of the probing virtual photon is small compared to the transverse jet energy. The calculation is based on the phase-space slicing method. The initial state singularity of the virtual photon is factorized into the structure function of the virtual photon, using the MS-bar factorization scheme for virtual photons. Numerical results are presented for LEP2 conditions. The perturbative stability of the pure direct virtual photon approach is compared to that of including resolved virtual photons in different regions of Q^2. We make predictions for cross sections which suggest that different parametrizations of virtual photon parton densities should be distinguishable by measurements of jet cross sections at LEP.Comment: 19 pages, 8 eps figue

Forward Jet Production at small x in Next-to-Leading Order QCD

The production of forward jets of transverse energy E_T\simeq Q and large momentum fraction x_jet >> x is calculated in next-to-leading order including consistently direct and resolved virtual photon contributions. The predictions are compared to recent ZEUS and H1 data. Good agreement with the data is found.Comment: 11 pages, 3 eps figues; text in 2.1 clearified, figure 2 slightly changed; version to appear in Phys. Lett.

Inclusive Jet Production with Virtual Photons in Next-to-Leading Order QCD

We present a next-to-leading order calculation for the virtual photoproduction of one and two jets in $ep$ collisions. Soft and collinear singularities are extracted using the phase space slicing method. The collinear photon initial state singularity depends logarithmically on the mass of the virtual photon and is absorbed into the virtual photon structure function. An $\overline{MS}$ factorization scheme is defined similarly to the real photon case. Numerical results are presented for HERA conditions using the Snowmass jet definition for inclusive single jet and dijet cross sections. We study the dependence of these cross sections on the transverse energies and rapidities of the jets. Finally, we compare the ratio of the experimentally defined resolved and direct cross sections with recent ZEUS data as a function of the photon virtuality $P^2$.Comment: LaTeX, 28 pages, 7 figure