Professor Claire Gwenlan

Abstract:

The calculation of cross-sections at Next-to-Leading order in QCD involves the integration over the final state phase space in order to cancel the infra-red divergences. For the calculation of cross sections for jet observables in deep-inelastic scattering or at hadron-hadron colliders this integration requires the Monte Carlo generation of a large number of event weights, and must be repeated for any calculation with a different choice of parton densities within the proton or different choice of factorisation or renormalisation scale. This makes the full calculation with many of the available parton density function error sets, or any iterative fit of the parton densities themselves, prohibitive in terms of the processing time required. A method for the a posteriori inclusion of the parton densities in the calculation is presented. In this method, the Monte Carlo weights from the integration over the hard-subprocess phase space are stored in a look-up table so that the full calculation need be performed only once, after which the cross section can be obtained with any parton density set by a fast convolution with the stored weights. A detailed example from inclusive jet production at the LHC is presented. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Abstract:

The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer is ready to detect muons produced in high energy proton-proton collisions. © 2010 CERN for the benefit of the ATLAS collaboration.

Abstract:

The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons. In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated contribution to the constant term of (0.290.04 ^0.05)% in the barrel and (0.540.04 ^0.06)% in the endcaps. The same data are used to measure the drift velocity of ionization electrons in liquid argon, which is found to be 4.61±0.07 mm/μs at 88.5 K and 1 kV/mm. © 2010 CERN for the benefit of the ATLAS collaboration.

Abstract:

Single- and double-differential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb-1. The measurement was performed at large values of the photon virtuality, Q2, between 125 and 20 000 GeV2. The jets were reconstructed with the kT cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, ET,Bjet, to be larger than 8 GeV. In addition, the invariant mass of the dijet system, Mjj, was required to be greater than 20 GeV. The cross sections are described by the predictions of next-to-leading-order QCD. © 2010 The Author(s).

Abstract:

Measurements of the cross sections for charged current deep inelastic scattering in e⁺p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with an integrated luminosity of 132 pb^-1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318 GeV. The total cross section is presented at positive and negative values of the longitudinal polarisation of the positron beams. The single-differential cross-sections dσ/dQ², dσ/dx and dσ/dy are presented for Q²>200 GeV². The reduced cross-section σ̃ is presented in the kinematic range 2002<60000 GeV² and 0.006

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