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:

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.