Laser-plasma accelerator group

Abstract:

Inclusive dijet and trijet production in deep inelastic ep scattering has been measured for 10 < Q² < 100  GeV² and low Bjorken x, 10^-4 < xBj < 10^-2. The data were taken at the HERA ep collider with centre-of-mass energy sqrt(s) = 318  GeV using the ZEUS detector and correspond to an integrated luminosity of 82  pb^-1. Jets were identified in the hadronic centre-of-mass (HCM) frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of dijet and trijet differential cross sections are presented as functions of Q², xBj, jet transverse energy, and jet pseudorapidity. As a further examination of low-xBj dynamics, multi-differential cross sections as functions of the jet correlations in transverse momenta, azimuthal angles, and pseudorapidity are also presented. Calculations at O (αs³) generally describe the trijet data well and improve the description of the dijet data compared to the calculation at O (αs²). © 2007 Elsevier B.V. All rights reserved.

Abstract:

The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E* T,jet > 4 GeV and the jet with the highest transverse energy was required to have E* T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η* jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data. © 2007 Springer-Verlag / Società Italiana di Fisica.

Abstract:

Results are presented on the generation of quasimonoenergetic electron beams with energy up to 1GeV using a 40TW laser and a 3.3 cm-long hydrogen-filled capillary discharge waveguide [1, 2]. Electron beams were not observed without a plasma channel, indicating that self-focusing alone could not be relied upon for effective guiding of the laser pulse. Results are presented of the electron beam spectra, and the dependence of the reliability of producing electron beams as a function of laser and plasma parameters. ©2007 IEEE.

Abstract:

A GeV-class laser-driven plasma-based wakefield accelerator has been realized at the Lawrence Berkeley National Laboratory (LBNL). The device consists of the 40 TW high repetition rate Ti:sapphire LOASIS laser system at LBNL and a gas-filled capillary discharge waveguide developed at Oxford University. The operation of the capillary discharge guided laser plasma wakefield accelerator with a capillary of 225 μm diameter and 33 mm in length was analyzed in detail. The input intensity dependence suggests that excessive self-injection causes increased beam loading leading to broadband lower energy electron beam generation. The trigger versus laser arrival timing dependence suggests that the plasma channel parameters can be tuned to reduce beam divergence. ©2007 IEEE.