Prof Roman Walczak

Abstract:

Inclusive jet differential cross sections have been measured in neutral current deep inelastic e +p scattering for boson virtualities Q 2 > 125 GeV 2. The data were taken using the ZEUS detector at HERA and correspond to an integrated luminosity of 38.6 pb -1. Jets were identified in the Breit frame using the longitudinally invariant k T cluster algorithm. Measurements of differential inclusive jet cross sections are presented as functions of jet transverse energy (E BT.jet), jet pseudorapidity and Q 2, for jets with E BT.jet > 8 GeV. Next-to-leading-order QCD calculations agree well with the measurements both at high Q 2 and high E BT.jet. The value of α s(M z), determined from an analysis of dσ/dQ 2 for Q 2 > 500 GeV 2, is α s(M Z=0.1212±0.0017 (stat.) +0.0023-0.0031 (syst.) +0.0028-0.0027(th.). © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Diffractive production of D*±(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb-1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*±(2010) meson is reconstructed in the decay channel D*+ → (D0 → K-π+)πs+ (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Diffractive dissociation of virtual photons, γ*p → Xp, has been studied in ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 < Q2 < 0.70 GeV2 and 3 < Q2 < 80 GeV2 with 3 < MX < 38 GeV, where MX is the mass of the hadronic final state. Diffractive events were selected by two methods: the first required the detection of the scattered proton in the ZEUS leading proton spectrometer (LPS); the second was based on the distribution of MX. The integrated luminosities of the low- and high-Q2 samples used in the LPS-based analysis are ≃ 0.9 pb-1 and ≃ 3.3 pb-1, respectively. The sample used for the MX-based analysis corresponds to an integrated luminosity of ≃ 6.2 pb-1. The dependence of the diffractive cross section on W, the virtual photon-proton centre-of-mass energy, and on Q2 is studied. In the low-Q2 range, the energy dependence is compatible with Regge theory and is used to determine the intercept of the Pomeron trajectory. The W dependence of the diffractive cross section exhibits no significant change from the low-Q2 to the high-Q2 region. In the low-Q2 range, little Q2 dependence is found, a significantly different behaviour from the rapidly falling cross section measured for Q2 > 3 GeV2. The ratio of the diffractive to the virtual photon-proton total cross section is studied as a function of W and Q2. Comparisons are made with a model based on perturbative QCD.