Abstract
Triple differential dijet cross sections in e^\pm p interactions are presented in the region of photon virtualities 25GeV, and pseudorapidities -2.5 < eta_1^*, eta_2^* <0. The measurements are made in the gamma^* p centre-of-mass frame, using an integrated luminosity of 57pb^-1. The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q^2 and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E_T jet production.
Highlights
IntroductionIn the case of electron-proton collisions, investigated in this Thesis, the jet cross sections are successfully described in most of the HERA kinematic range by next-to-leading (NLO) Quantum Chromodynamics (QCD) calculations [H101a, H101c, H102a, H103a, ZEUS02b, ZEUS02c, ZEUS03b, ZEUS03a, H103b, H102b, ZEUS02a, H101b]
The analyses of jet production in various high energy processes have become a major field for testing perturbative Quantum Chromodynamics (QCD)
In doing that we use NLO QCD calculations as well as LO calculations supplemented with parton showers, which take into account leading logarithmic contributions to all orders
Summary
In the case of electron-proton collisions, investigated in this Thesis, the jet cross sections are successfully described in most of the HERA kinematic range by next-to-leading (NLO) QCD calculations [H101a, H101c, H102a, H103a, ZEUS02b, ZEUS02c, ZEUS03b, ZEUS03a, H103b, H102b, ZEUS02a, H101b]. The present analysis describes a new measurement of the dijet cross sections together with detailed comparisons of the data with available perturbative QCD calculations in order to identify which of them describe the data in which region. The measurement of dijet production is suitable for the investigation of effects related to photon structure, which has been studied during the last two decades in e+e− and ep collisions (for comprehensive surveys of present data on photon structure and related issues see [KZS01, Nis00]). In the direct photon process, the photon interacts as a whole with a parton from the proton, whereas in the resolved photon process, it behaves as a source of partons, which subsequently interact with partons from the proton
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