ATLAS

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:

We examine why a probabilistic approach to modelling the various components of spatial language is the most practical for spatial algorithms in which they can be employed, and examine such models for prepositions such as ̀between' and ̀by'. We provide an example of such a probabilistic treatment by exploring a novel application of spatial models to the induction of the occupancy of an object in space given a description about it.

Abstract:

The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays. © 2010 CERN for the benefit of the CMS collaboration.

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.