Laser-plasma accelerator group

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 ^B T.jet), jet pseudorapidity and Q ², for jets with E ^B T.jet > 8 GeV. Next-to-leading-order QCD calculations agree well with the measurements both at high Q ² and high E ^B T.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:

We report guiding of laser pulses with peak input intensities greater than 10(17) W cm(-2) in 30 mm and 50 mm long H2-filled capillary discharge waveguides. Under conditions producing good guiding the coupling and propagation losses of the waveguide were <4% and (7+/-1) m(-1), respectively. The spectra of the transmitted pulses were not broadened significantly, but were shifted to shorter wavelength. It is concluded that this shift is not associated with significant temporal distortion of the laser pulse.

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.