Charm Production and QCD Analysis at HERA and LHC

In this thesis the study of charm production in ep and pp collisions is presented. The heavy- quark masses provide a hard scale, allowing the application of perturbative QCD. A measurement of D + -meson production in deep inelastic scattering with the ZEUS detector at HERA is presented. The analysis was performed using a data sample with an integrated luminosity of 354 pb-1. Di erential cross sections were measured as a function of virtuality Q 2 , inelasticity y , transverse momentum and pseudorapidity of the D + mesons. Lifetime infor- mation was used to reduce the combinatorial background significantly. Next-to-leading-order QCD predictions in the fixed-flavour-number scheme were compared to the data. This measurement was combined with other H1 and ZEUS measurements of charm produc- tion. The combination was performed at inclusive level for the reduced charm cross sections, which were obtained from the measured visible cross sections, extrapolated to the full phase space using the shape of the theoretical predictions in the fixed-flavour-number scheme. The combination method accounts for the correlations of the systematic uncertainties among the di erent datasets, thus allowing cross calibration of di erent measurements. The combined charm data were compared to QCD predictions in various heavy-flavour schemes and used to- gether with the inclusive production data at HERA as input for QCD analyses to determine the charm running mass in the MS renormalisation scheme and the optimal values of the charm- quark mass parameters in other heavy-flavour schemes. An additional combination of the H1 and ZEUS D + visible cross sections was performed to provide the combined cross sections without theory-related uncertainties from the extrapola- tion procedure. This combination also provides di erential cross sections as a function of the D + kinematic variables. Next-to-leading-order QCD predictions in the fixed-flavour-number scheme were compared to the combined D + cross sections and a ‘customised’ QCD calcu- lation was introduced in order to improve the agreement between the central values of the theoretical predictions and the data. While the HERA charm data are sensitive to the gluon distribution in the proton at the values of partonic fractions of the proton momenta 10-4 . x . 10-1, the production of charm quarks at LHCb probes the region 5 10-6 x . 10-4. The impact of recent LHCb measurements of heavy-flavour production on parton distribution functions was studied in a QCD analysis in the fixed-flavour-number scheme at next-to-leading order. Di erential cross sections of charm and beauty production obtained by the LHCb experiment were used together with the combined inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose constraints on the gluon and sea-quark distributions at very low partonic fractions of the proton momenta. This kinematic range is currently not covered by other experimental data in QCD fits. As the technical part of this thesis, the ZEUS Event Display program has been modified in the context of the ZEUS data preservation project to become independent of the ZEUS Soft- ware. The new program is a pure ROOT application. While it provides the main functionalities that were available in the classic program, it does not require any maintenance.