Laser-plasma accelerator group

Abstract:

Cross sections for e⁺p charged current deep inelastic scattering at a centre-of-mass energy of 318 GeV have been determined with an integrated luminosity of 60.9 pb^-1 collected with the ZEUS detector at HERA. The differential cross sections dσ/dQ², dσ/dx and dσ/dy for Q² > 200 GeV2 are presented. In addition, d²σ/dxdQ² has been measured in the kinematic range 280 GeV² < Q² < 17 000 GeV² and 0.008 < x < 0.42. The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson propagator is determined to be MW = 78.9 ± 2.0 (stat.) ± 1.8 (syst.) -1.8^+2.0 (PDF) GeV from a fit to dσ/dQ². The chiral structure of the Standard Model is also investigated in terms of the (1-y)² dependence of the double-differential cross section. The structure-function F2^CC has been extracted by combining the measurements presented here with previous ZEUS results from e^-p scattering, extending the measurement obtained in a neutrino-nucleus scattering experiment to a significantly higher Q² region.

Abstract:

Production of D^*±(2010) mesons in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^-1. Diffractive events were identified by the presence of a large rapidity gap in the final state. Differential cross sections have been measured in the kinematic region 1.52<200 GeV², 0.02P<0.035, β<0.8, pT(D^*±)>1.5 GeV and η(D^*±) <1.5. The measured cross sections are compared to theoretical predictions. The results are presented in terms of the open-charm contribution to the diffractive proton structure function. The data demonstrate a strong sensitivity to the diffractive parton densities. © 2003 Published by Elsevier B.V.

Abstract:

The production rates and substructure of jets have been studied in charged current deep inelastic e⁺p scattering for Q² > 200 GeV² with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb^-1. Inclusive jet cross sections are presented for jets with transverse energies ET^jet > 14 GeV and pseudorapidities in the range -1 < η^jet < 2. Dijet cross sections are presented for events with a jet having ET^jet > 14 GeV and a second jet having ET^jet > 5 GeV. Measurements of the mean subjet multiplicity, 〈ηsbj〉, of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of αs (MZ), determined from 〈ηsbj〉 at ycut = 10^-2 for jets with 25 < ET^jet < 119 GeV, is α s (MZ) = 0.1202 ± 0.0052 (stat.) -0.0019^+0.0060 (syst.)-0.0053 ^+0.0065 (th.). The mean subjet multiplicity as a function of Q ² is found to be consistent with that measured in NC DIS.

Abstract:

A molecular-dynamic (MD) code for calculating the relaxation of an arbitrary electron energy distribution in a plasma was described. The MD approach provided a more fundamental set of equations, with fewer assumptions. The accuracy of the MD approach was proved by comparing its results with the Monte Carlo and Fokker-Planck codes using a set of plasma parameters for which the Fokker-Planck calculation gave incorrect results. Calculating energy relaxation in plasmas proved important for the understanding of the operation of new types of short-wavelength lasers based on optical field ionization.