ATLAS

Abstract:

The J/ψ decay angular distributions have been measured in inelastic photo-production in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb-1. The range in photon-proton centre-of-mass energy, W, was 50 < W < 180 GeV. The J/ψ mesons were identified through their decay into muon pairs. The polar and azimuthal angles of the μ+ were measured in the J/ψ rest frame and compared to theoretical predictions at leading and next-to-leading order in QCD. © SISSA 2009.

Abstract:

Events with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb-1. The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e+p collision data with a scalar sum of the lepton transverse momenta above 100GeV while 1.94 ± 0.17 events are expected. Such events are not observed in e-p collisions for which 1.19 ± 0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions. © SISSA 2009.

Abstract:

The CRESST experiment aims for a detection of dark matter in the form of WIMPs. These particles are expected to scatter elastically off the nuclei of a target material, thereby depositing energy on the recoiling nucleus. CRESST uses scintillating CaW04 crystals as such a target. The energy deposited by an interacting particle is primarily converted to phonons which are detected by transition edge sensors. In addition, a small fraction of the interaction energy is emitted from the crystals in the form of scintillation light which is measured in coincidence with the phonon signal by a separate cryogenic light detector for each target crystal. The ratio of light to phonon energy permits the discrimination between the nuclear recoils expected from WIMPs and events from radioactive backgrounds which primarily lead to electron recoils. CRESST has shown the success of this method in a commissioning run in 2007 and, since then, further investigated possibilities for an even better suppression of backgrounds. Here, we report on a new class of background events observed in the course of this work. The consequences of this observation are discussed and we present the current status of the experiment. © 2009 American Institute of Physics.

Abstract:

A luminosity upgrade is planned in the future for the Large Hadron Collider at CERN (called SLHC). Two optical fibres have been tested in a bespoke cold container achieving a constant temperature of ≃ -25°C during the entire exposure. The motivations and results of these tests are presented and two mul-timode and one single mode optical fibre have been identified as candidates for optical links within the joint ATLAS and CMS Versatile Link project.

Abstract:

The electroweak theory elegantly combines the electromagnetic and weak forces, explaining a wide range of interactions using a gauge theory with just three parameters. The theory predicted the W and Z weak gauge bosons before they were directly observed in 1983, and its detailed predictions of W and Z boson properties have been tested to such precision that they now serve as probes for new particles through loop-level interactions. Currently, the limiting parameter in these probes is the W boson mass, whose uncertainty has been recently reduced by measurements of √s = 1.96 TeV pp collision data produced by the Fermilab Tevatron. Future measurements at the Tevatron and the Large Hadron Collider will result in nearly a factor of three reduction in the uncertainty on the W boson mass, significantly constraining the Higgs boson mass and the masses and couplings of supersymmetric particles. Other W and Z boson properties recently constrained by measurements at the Tevatron and HERA include their self-couplings and couplings to quarks. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.