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Abstract:

Deep inelastic scattering and its diffractive component, e p → e^′ γ^* p → e^′ X N, have been studied at HERA with the ZEUS detector using an integrated luminosity of 52.4 pb^-1. The MX method has been used to extract the diffractive contribution. A wide range in the centre-of-mass energy W (37-245 GeV), photon virtuality Q² (20-450 GeV²) and mass MX (0.28-35 GeV) is covered. The diffractive cross section for 2 < MX < 15 GeV rises strongly with W, the rise becoming steeper as Q² increases. The data are also presented in terms of the diffractive structure function, F2^{D (3)}, of the proton. For fixed Q² and fixed MX, xP F2^{D (3)} shows a strong rise as xP → 0, where xP is the fraction of the proton momentum carried by the pomeron. For Bjorken-x < 1 × 10^-3, xP F2^{D (3)} shows positive log Q² scaling violations, while for x ≥ 5 × 10^-3 negative scaling violations are observed. The diffractive structure function is compatible with being leading twist. The data show that Regge factorisation is broken. © 2008 Elsevier B.V. All rights reserved.

Abstract:

Jet cross sections were measured in charged-current deep inelastic e±p scattering at high boson virtualities Q2 with the ZEUS detector at HERA II using an integrated luminosity of 0.36fb-1. Differential cross sections are presented for inclusive-jet production as functions of Q2, Bjorken x and the jet transverse energy and pseudorapidity. The dijet invariant mass cross section is also presented. Observation of three- and four-jet events in charged-current e±p processes is reported for the first time. The predictions of next-to-leading-order (NLO) QCD calculations are compared to the measurements. The measured inclusive-jet cross sections are well described in shape and normalization by the NLO predictions. The data have the potential to constrain the u and d valence-quark distributions in the proton if included as input to global fits. © 2008 The American Physical Society.