Heaphy, Eileen Anne; (2002) Jet photoproduction and photon structure. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Events containing two and three jets have been studied in photoproduction at HERA. The data were taken with the ZEUS detector during 1996 and 1997 in a photon-proton centre-of-mass energy range 134-277 GeV. Differential cross sections are presented in limited kinematic regions including, for the first time at ZEUS, that with respect to the fraction of the incoming photon momentum participating in the production of the jets, xyobs. Two-jet events were required to contain at least two jets with transverse energy greater than 14 GeV and 11 GeV, in the pseudorapidity region -1 < njet < 2.4. Their measurements are com pared to next-to-leading-order QCD predictions with three different parametrisations for the photon parton densities. None of the predictions describe the data adequately, even when theoretical uncertainties are taken into account. The three-jet cross section is defined for events with at least three jets in the region -1 < njet < 2 and with an an invariant mass greater than 50 GeV. It has been measured and compared with fixed order parton shower Monte Carlo calculations and leading-order QCD predictions. Both models described the shape of the distributions adequately, despite the lack of higher orders. The scattering angle of the most energetic jet in the three-jet rest frame has been investigated and shows some sensitivity to both the photon and proton parton distributions.

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