Joerg Behr (Hamburg University)
Jet cross sections in deep inelastic ep scattering (DIS) and photoproduction were measured with the H1 and ZEUS detectors at HERA using data collected in the years 1999-2007 and corresponding to an integrated luminosity of up to 500 pb-1. Measurements of differential cross sections for inclusive-jet production in DIS and photoproduction are presented together with the tri-jet to di-jet ratio in DIS. Inclusive jet, di-jet and tri-jet cross sections, normalised to the neutral current DIS cross sections, are also measured and presented as functions of Q^2, jet transverse momentum and proton momentum fraction. All the measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. QCD analyses of the measured observables were used to extract precise values of the strong coupling constant and test its energy-scale dependence.