Jets in photoproduction at HERA

Dijet and three-jet cross sections as functions of various jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e+p data collected from 1995-97 with an integrated luminosity of 34.9 pb-1. Jets are found using the inclusive k perpendicularto algorithm with a minimum transverse momentum of the highest transverse momentum jet of 25 GeV. The phase space covers high longitudinal proton momentum fractions 0.05<xp<0.6 and high photon longitudinal momentum fractions 0.1<xγ<1. The results are compared to the predictions of leading order and next-to-leading order perturbative QCD including current photon and proton parton densities. The dijet cross sections are found to be compatible in a wide kinematical range. At low xγ the 3-jet cross sections show deviations from the predictions of leading-order QCD. (orig.)