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Expected Performance of the ATLAS Experiment: Detector, Trigger and Physics

2011-12-22T13:42:41Z

Expected Performance of the ATLAS Experiment: Detector, Trigger and Physics Aad, G.; Bacci, Cesare; Ceradini, Filippo; Di Luise, Silvestro; Diglio, Sara; Orestano, Domizia; Pastore, Fernanda; Petrucci, Fabrizio; Spogli, L.; et, al. 2009-01 The Large Hadron Collider (LHC) at CERN promises a major step forward in the understanding of the fundamental nature of matter. The ATLAS experiment is a general-purpose detector for the LHC, whose design was guided by the need to accommodate the wide spectrum of possible physics signatures. The major remit of the ATLAS experiment is the exploration of the TeV mass scale where ground breaking discoveries are expected. In the focus are the investigation of the electroweak symmetry breaking and linked to this the search for the Higgs boson as well as the search for Physics beyond the Standard Model. In this report a detailed examination of the expected performance of the ATLAS detector is provided, with a major aim being to investigate the experimental sensitivity to a wide range of measurements and potential observations of new physical processes. An earlier summary of the expected capabilities of ATLAS was compiled in 1999. Since that time, the design of the detector has been finalised, and construction and installation have been completed. An extensive test-beam programme was undertaken. Furthermore, the simulation and reconstruction software code and frameworks have been completely rewritten. Revisions incorporated reflect improved detector modelling as well as major technical changes to the software technology. Greatly improved understanding of calibration and alignment techniques, and their practical impact on performance, is now in place. The studies reported here are based on full simulations of the ATLAS detector response. A variety of event generators were employed. The simulation and reconstruction of these large event samples thus provided an important operational test of the new ATLAS software system. In addition, the processing was distributed world-wide over the ATLAS Grid facilities and hence provided an important test of the ATLAS computing system – this is the origin of the expression “CSC studies” (“computing system commissioning”), which is occasionally referred to in these volumes. This report is broadly divided into two parts: firstly the performance for identification of physics objects is examined in detail, followed by a detailed assessment of the performance of the trigger system. This part is subdivided into chapters surveying the capabilities for charged particle tracking, each of electron/photon, muon and tau identification, jet and missing transverse energy reconstruction, b-tagging algorithms and performance, and finally the trigger system performance. The second major subdivision of the report addresses physics measurement capabilities, and new physics search sensitivities. Individual chapters in this part discuss ATLAS physics capabilities in Standard Model QCD and electroweak processes, in the top quark sector, in b-physics, in searches for Higgs bosons, supersymmetry searches, and finally searches for other new particles predicted in more exotic models.

In-Situ Determination of the Performance of the Muon Spectrometer

2011-12-22T13:40:40Z

In-Situ Determination of the Performance of the Muon Spectrometer Diglio, Sara; Orestano, Domizia; Petrucci, Fabrizio; Spogli, Luca 2009 Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics 208-228 The ATLAS muon spectrometer consists of three layers of precision drift-tube chambers in a toroidal magnetic with a field integral between 2.5 and 6 Tm. Muon tracks are reconstructed with 97% efficiency and a momentum resolution between 3% and 4% for 10 GeV< pT <500 GeV and better than 10% for transverse momenta up to 1 TeV. In this note, the performance of a perfectly calibrated and aligned muon spectrometer will be reviewed and the impact of deteriorations of the magnetic field, the calibration and misalignment of the muon chambers on the performance will be discussed. The main part of the note describes how the performance of the muon spectrometer can be determined using dimuon decays of Z bosons and JPsi mesons

A design study of the production of Z bosons in association with b jet in final states with muons with the ATLAS detector at the LHC

2011-06-28T00:01:10Z

A design study of the production of Z bosons in association with b jet in final states with muons with the ATLAS detector at the LHC Diglio, Sara 2009-01-22 The Large Hadron Collider (LHC) is the machine that will provide the highest ever produced energy in the center of mass, reaching the value of s=14 TeV for proton-proton collisions and giving the possibility to produce particles with mass up to few TeV. The work presented in this thesis is carried on in the framework of one of the LHC experiments: the ATLAS experiment. It presents a study of the prospects for measuring the pp ¡ Z + b jet + X channel (where X states for everything in the final state produced in association to the leading process) considering the decay selection Z ¡ µ¢ µ£ and the identification of the b jet in an inclusive mode and through the semi-leptonic decay of the b jet into muons. This process is interested in its own and also as background for many Standard Model and beyond Standard Model physics processes. The wide kinematic range for production of Z + b jet serves as a testing ground for perturbative QCD predictions. In addition the cross section is sensitive to the b quark content in the proton and its precise measurement will help in reducing the current uncertainty on the partonic content of the proton (PDF's). Such uncertainty is presently affecting the potential for discovering new physics at LHC. The main aim of this work has been to develop analysis techniques in order to evaluate the contamination of the signal from backgrounds and to study possible methods to extract signal from such backgrounds. The study was performed using the signal and background events modelled with Monte Carlo generators. Full and fast simulation of the Atlas detector was performed to obtain realistic estimates of the sensitivity of the measurements. An estimation of the main contributors to the systematic uncertainties on signal cross section measurement has also been provided.