Measurement of inclusive jet cross-sections in photon-proton collisions at HERA

This thesis presents a measurement of inclusive high E_T^jet (≥ 21 GeV) jet production cross-sections in quasi-real photoproduction, based on 24.1 pb^-1 of e + p data collected by H1 in 1996-1997. The kinematic range of the measurement corresponds to Q² ≤ 1 GeV² and 95 ≤ W ≤ 285 GeV. The jets were found in the pseudorapidity range -1 ≤ η^jet ≤ 2.5 using the inclusive k_T algorithm in the laboratory frame. Measured cross-sections were corrected to the hadron level, and compared to LO and NLO QCD calculations. The measured distributions are well described, both in normalisation and shape, by NLO QCD predictions using various available photon and proton parton density functions (PDFs). The hadronization corrections to the NLO QCD calculations only slightly improve the agreement with the data. The current precision of the experimental results as well as of the theoretical predictions does not allow one to discriminate between the different PDFs. A new measurement at low E_T^jet (≥ 5 GeV), based on 0.47 pb^-1 of tagged (Q² ≤ 0.01 GeV²) minimum bias data is also presented. The E_T^jet spectrum obtained from both low and high E_T^jet data samples is well reproduced by NLO QCD calculations. A fit by a QCD-inspired power law gives consistent results with previous similar measurements. LO QCD Monte Carlo calculations, which include initial and final state leading logarithm parton showers, hadronization and additional interactions of spectator partons in the resolved gamma + p collisions, describe the shape of the measured distributions. Finally, the data are compared with similar results obtained at p-pbar colliders. (author)