Laser-plasma accelerator group

Abstract:

Bose-Einstein correlations in one and two dimensions have been studied in deep inelastic ep scattering events measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb^-1. The correlations are independent of the virtuality of the exchanged photon, Q², in the range 0.1 < Q² < 8000 GeV². There is no significant difference between the correlations in the current and target regions of the Breit frame for Q² > 100 GeV². The two-dimensional shape of the particle-production source was investigated, and a significant difference between the transverse and the longitudinal dimensions of the source is observed. This difference also shows no Q² dependence. The results demonstrate that Bose-Einstein interference, and hence the size of the particle-production source, is insensitive to the hard subprocess. © 2004 Published by Elsevier B.V.

Abstract:

A search for events containing isolated tau leptons and large missing transverse momentum, not originating from the tau decay, has been performed with the ZEUS detector at the electron-proton collider HERA, using 130 pb ^-1 of integrated luminosity. A search was made for isolated tracks coming from hadronic tau decays. Observables based on the internal jet structure were exploited to discriminate between tau decays and quark- or gluon-induced jets. Three tau candidates were found, while 0.40 -0.13^+0.12 were expected from Standard Model processes, such as charged current deep inelastic scattering and single W ^±-boson production. To search for heavy-particle decays, a more restrictive selection was applied to isolate tau leptons produced together with a hadronic final state with high transverse momentum. Two candidate events survive, while 0.20±0.05 events are expected from Standard Model processes. © 2004 Published by Elsevier B.V.

Abstract:

The results of the first experimental demonstration of a short-wavelength laser driven within a gas-filled capillary-discharge waveguide were described. The xenon gas was mixed with the hydrogen and strong lasing on the 4d 95d-4d95p transition in Xe8+ at 41.8 nm was observed. Analysis shows that lasing was strongly correlated with good guiding of the pump pulse and numerical simulations indicate that gain is likely to have been achieved over a significant fraction of the 30 mm length of the capillary. The success of this proof-of-principle experiment suggests that this and other short-wavelength lasers could be driven within waveguides of this type, leading to increased energy output and reduced beam divergence.

Abstract:

Cross sections for e+ p neutral current deep inelastic scattering have been measured at a center-of-mass energy of √s = 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 63.2 pb -1. The double-differential cross section, d2σ/ dxdQ2, is presented for 200 GeV2 < Q2 < 30 000 GeV2 and for 0.005 < x < 0.65. The single-differential cross sections dσ/dQ2, dσ/dx and dσ/dy are presented for Q2 > 200 GeV2. The effect of Z-boson-exchange is seen in dσ/dx measured for Q2 > 10 000 GeV2. The data presented here were combined with ZEUS e+ p neutral current data taken at √s = 300 GeV and the structure function F2em was extracted. All results agree well with the predictions of the Standard Model.

Abstract:

Inclusive Ks⁰Ks⁰ production in deep inelastic ep scattering at HERA has been studied with the ZEUS detector using an integrated luminosity of 120 pb^-1. Two states are observed at masses of 1537-8^-9 MeV and 1726 ± 7 MeV, as well as an enhancement around 1300 MeV. The state at 1537 MeV is consistent with the well established f′2(1525). The state at 1726 MeV may be the glueball candidate f0(1710). However, it's width of 38 -14^-20 MeV is narrower than 125 ± 10 MeV observed by previous experiments for the f0(1710). © 2003 Elsevier B.V. All rights reserved.