Laser-plasma accelerator group

Abstract:

Laser driven wakefield accelerators produce accelerating fields thousands of times those achievable in conventional radio-frequency accelerators, offering compactness and ultrafast bunches to potentially extend the frontiers of high energy physics and enable laboratory scale ultrafast radiation sources. Realization of this potential requires understanding of accelerator physics to advance beam performance and stability, and particle simulations model the highly nonlinear, kinetic physics required. One-to-one simulations of experiments provide new insight for optimization and development of 100 MeV to GeV and beyond laser accelerator stages, and on production of reproducible and controllable low energy spread beams with improved emittance (focusability) and energy through control of injection. © 2007 IOP Publishing Ltd.

Abstract:

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. Charm has been tagged by reconstructing D*+, D0, D+ and D+s (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range pT (D* +,D 0,D+) > 3GeV, pT (D+s ) > 2GeV and |η(D)| < 1.6 for 1.5 < Q2 < 1000GeV2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in pT (D) and η(D) in order to determine the open-charm contribution, Fcc2 (x,Q2), to the proton structure function F2. © SISSA 2007.

Abstract:

The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic ep scattering using an integrated luminosity of 45 pb^-1 taken with the ZEUS detector. The kinematic range is 1002<8000 GeV ², 0.22 is the virtuality of the exchanged boson, y is the inelasticity and x is the Bjorken variable. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data. © Springer-Verlag Berlin Heidelberg 2007.

Abstract:

A new scheme for quasi-phasematching high harmonic generation (HHG) in gases is proposed. In this, the rapid variation of the axial intensity resulting from excitation of more than one mode of a waveguide is used to achieve quasi phasematching. Numerical modeling demonstrates enhancement of the harmonic signal over that achieved for a single coherence length by factors >10 ⁴. © 2007 Optical Society of America.

Abstract:

The production of the neutral strange hadrons K⁰ S, Λ and Λ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, Λ (Λ) asymmetry and polarization have been measured in three kinematic regions: Q² > 25 GeV²; 5 < Q² < 25 GeV²; and in photoproduction (Q ² 0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at e⁺e^- colliders, except for an enhancement of baryon relative to meson production in photoproduction. © Springer-Verlag / Società Italiana di Fisica 2007.