Laser-plasma accelerator group

Abstract:

A high harmonic optical generator comprising a laser arrangement for emitting a beam of polarized radiation at a fundamental frequency and an optical waveguide having a hollow core for a gaseous harmonic generation medium for the generation of high harmonics of the fundamental frequency, the optical waveguide having an optical propagation axis along the hollow core, the laser arrangement is configured to couple the beam of polarized radiation along the propagation axis of the hollow core optical waveguide to provide a beam of optical driving radiation for the high harmonic generation, the optical driving radiation having a plane of polarization that rotates about the propagation axis.

Abstract:

A scheme for quasi-phase-matching high-harmonic generation is proposed in which polarization beating within a hollow core birefringent waveguide modulates the generation of harmonics. The evolution of the polarization of a laser pulse propagating in a birefringent waveguide is calculated and is shown to periodically modulate the harmonic generation process. The optimum conditions for achieving quasi-phase-matching using this scheme are explored and the growth of the harmonic intensity as a function of experimental parameters is investigated.

Abstract:

A high harmonic optical generator comprising a laser arrangement and an optical waveguide, wherein the laser arrangement is configured to couple a beam of linearly polarized radiation at a fundamental frequency into the optical waveguide to provide a beam of optical driving radiation that propagates along a propagation axis of the optical waveguide, the optical waveguide has a hollow core for a gaseous harmonic generation medium for generation of high harmonics of the fundamental frequency, and the generator is configured for the driving radiation to have a polarization ellipticity that periodically varies along the propagation axis of the optical waveguide.

Abstract:

Scaled momentum distributions for the strange hadrons K S0 and ∧/∧were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb -1. The evolution of these distributions with the photon virtuality, Q 2, was studied in the kinematic region 10 < Q 2 < 40000 GeV 2 and 0.001 < x < 0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Nextto-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e +e - data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e +e -, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, anti-quarks and gluons yielding K S0 and ∧/∧ strange hadrons. © SISSA 2012.

Abstract:

Three-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to 127pb-1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixed-order perturbative calculations assuming the values of the color factors CF, CA, and TF as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic ep scattering and photoproduction regimes are consistent with the admixture of color configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N. © 2012 American Physical Society.