Laser-plasma accelerator group

Abstract:

The results of a study of the channeling of intense picosecond laser pulses by a discharge-ablated capillary waveguide are presented. The peak-energy transmission for a 10-mm-long waveguide is measured to be 65% for an input intensity of 1 × 10¹⁶ W cm^-2. The importance of inverse bremsstrahlung, stimulated Raman scattering, stimulated Brillouin scattering, atomic modulation instabilities, and ionization of the discharge plasma as loss mechanisms for both intense femtosecond and picosecond pulses are considered. © 2000 Optical Society of America.

Abstract:

Presented is a novel approach for driving short-wavelength lasers, with good prospects for scaling to shorter wavelengths. Present investigations include analysis of extensions to other transitions such as the 3s → 3p and 3p → 3d hole transitions in Ni-like ions following monopole excitation of 3s and 3p holes in OFI plasmas. The results of those calculations are presented.

Abstract:

The production of D*^± (2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The decay channels D*⁺ → D⁰π⁺ (+c.c.), with D⁰ → K^-π⁺ or D⁰ → K^-π^-π⁺π⁺, have been used to identify the D mesons. The e⁺p cross section for inclusive D*^± production with 1 < Q² < 600 GeV² and 0.02 < y < 0.7 is 8.31±0.31(stat.)^+0.30 -0.50 (syst.) nb in the kinematic region 1.5 < pT(D*^±) < 15 GeV and \η(D*^±)\ < 1.5. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pT(D*^±) and η(D*^±) in order to determine the charm contribution, F^cc̄ 2 (x, Q²), to the proton structure function. The ratio F^cc̄ 2/F2 rises from ≃10% at Q² ≃ 1.8GeV² to ≃30% at Q² ≃130GeV² for x values in the range 10^-4 to 10^-3.

Abstract:

The e+p charged-current deep inelastic scattering cross sections, dσ/dQ2 for Q2 between 200 and 60000 GeV2, and dσ/dx and dσ/dy for Q2 > 200 GeV2, have been measured with the ZEUS detector at HERA. A data sample of 47.7 pb-1, collected at a center-of-mass energy of 300 GeV, has been used. The double-differential cross-section dσ/dQ2 falls by a factor of about 50000 as Q2 increases from 280 to 30000 GeV2. The double differential cross section d2σ/dxdQ2 has also been measured. A comparison between the data and Standard Model (SM) predictions shows that contributions from antiquarks (ū and c̄) and quarks (d and s) are both required by the data. The predictions of the SM give a good description of the full body of the data presented here. A comparison of the charged-current cross-section dσ/dQ2 with the recent ZEUS results for neutral-current scattering shows that the weak and electromagnetic forces have similar strengths for Q2 above M2W, M2Z. A fit to the data for dσ/dQ2 with the Fermi constant GF and MW as free parameters yields GF = (1.171±0.034 (stat.)+0.026-0.032 (syst.)+0.016-0.015 (PDF)) × 10-5 Gev-2 and MW = 80.8+4.9-4.5 (stat.)+5.0-4.3(syst.)+1.4-1.3 (PDF) GeV. Results For MW, where the propagator effect alone or the SM constraint between GF and MW have been considered, are also presented.