A combination is presented of the inclusive deep inelastic cross sections measured by the H1 and ZEUS Collaborations in neutral and charged current unpolarised e ± p scattering at HERA during the period 1994-2000. The data span six orders of magnitude in negative four-momentum-transfer squared, Q 2 , and in Bjorken x. The combination method used takes the correlations of systematic uncertainties into account, resulting in an improved accuracy. The combined data are the sole input in a NLO QCD analysis which determines a new set of parton distributions, HERAPDF1.0, with small experimental uncertainties. This set includes an estimate of the model and parametrisation uncertainties of the fit result.

Beauty production in deep inelastic scattering with events in which a muon and a jet are observed in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114 pb −1 . The fraction of events with beauty quarks in the data was determined using the distribution of the transverse momentum of the muon relative to the jet. The cross section for beauty production was measured in the kinematic range of photon virtuality, Q 2 > 2 GeV 2 , and inelasticity, 0.05 < y < 0.7, with the requirement of a muon and a jet. Total and differential cross sections are presented and compared to QCD predictions. The beauty contribution to the structure function F 2 was extracted and is compared to theoretical predictions.

Abstract. Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb −1 . The measurements were made in the kinematic range Q 2 < 1 GeV 2 , 0.20 < y < 0.85 and x IP < 0.025, where Q 2 is the photon virtuality, y is the inelasticity and x IP is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E jet T , were required to satisfy E jet T > 7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range −1.5 < η jet < 1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.

The production of charm and beauty quarks in ep interactions has been measured with the ZEUS detector at HERA for squared four-momentum exchange Q 2 > 20 GeV 2 , using an integrated luminosity of 126 pb −1 .Charm and beauty quarks were identified through their decays into muons. Differential cross sections were measured

In order to extend the tracking acceptance, to improve the primary and secondary vertex reconstruction and thus enhancing the tagging capabilities for short lived particles, the ZEUS experiment at the HERA Collider at DESY installed a silicon strip vertex detector. The barrel part of the detector is a 63 cm long cylinder with silicon sensors arranged around an elliptical beampipe. The forward part consists of four circular shaped disks. In total just over 200k channels are read out using 2.9 m(2) of silicon. In this report a detailed overview of the design and construction of the detector is given and the performance of the completed system is reviewed