Measurement of beauty quark production in deep inelastic scattering at HERA

In this dissertation the measurement of beauty quark (or b-quark) production in deep inelastic electron-proton collisions at HERA is presented. The measurement is based on the data collected by the ZEUS experiment during the years 1999-2000 and corresponds to an integrated luminosity of 60 pb-1. The reaction is e+ p → e+ b anti b X → e+ μ Jet X, where at least one of the b-quarks decays semi-leptonically into a muon and a jet. Events are selected containing the scattered positron, a hard jet reconstructed in the Breit frame and a muon traversing the barrel and rear muon chambers of the ZEUS experiment. The fraction of events from b-decays is extracted on a statistical basis using the distribution of the muon transverse momentum relative to the closest jet. QCD predictions to the next-to-leading order (NLO) accuracy are obtained for this process and a detailed analysis of the NLO QCD uncertainties is carried out. Both the total and single differential cross sections are almost a factor 1.4 above the NLO QCD predictions but compatible within the experimental and theoretical uncertainties. The result is also compatible with the prediction of the CASCADE Monte Carlo program, based on kT-factorization and CCFM QCD evolution equation. Other Monte Carlo predictions lie below the data. A more precise measurement of beauty quark production will be possible after the luminosity upgrade of the HERA collider. To fully benefit from the new experimental conditions, the ZEUS detector was upgraded by an improved tracking system consisting of a Straw Tube Tracker and a silicon micro vertex detector (MVD). The latter device will allow a precise reconstruction of the heavy meson decays. In this dissertation the results of test beam measurements performed on the MVD half modules are presented. The charge collection, the signal/noise ratio and the hit resolution are measured for different incidence angles using existing and newly developed hit reconstruction algorithms. Detailed studies of the charge sharing mechanism are performed on the regions of the MVD sensors corresponding to the bonding pads and on the overlap between single sensors. (orig.)