Muons in the ATLAS detector are reconstructed by combining the information from the two tracking devices: the Inner Detector and the Muon Spectrometer (MS), located in the outermost part of the ...experiment. Until they reach the MS, muons traverse typically 100 radiation lengths (X0) of material, most part instrumented by the electromagnetic and hadronic calorimeters. The proper account for multiple scattering and energy loss effects is essential for the reconstruction and the use of the calorimeter measurement can improve the transverse momentum resolution, specially in case of high energy deposits. On the other hand, the calorimeter activity around a muon, or conversely its isolation, is one of the most powerful features to distinguish W and Z decays from semi-leptonic decays of heavy flavour mesons (containing b and c quarks). The principle of the software package that performs these tasks, called TrackInCaloTools is presented together with the expected performance in physics analyses.
The ATLAS experiment designed to exploit the full discovery potential of the Large Hadron Collider (LHC) at CERN, is currently being assembled and tested. Its Muon Spectrometer designed to measure ...muons in the final state from proton-proton interactions at the LHC with good momentum resolution (from 3% - 11% for muons of momentum of 1TeV), is being commissioned at the ATLAS cavern. It consists of four types of detectors, each using a different technology. Throughout this paper, a brief description of the commissioning procedure, the software tools developed and the first results obtained is given.
ATLAS is one of the four experiments at the Large Hadron Collider (LHC) at CERN. This experiment has been designed to study a large range of physics including searches for previously unobserved ...phenomena such as the Higgs Boson and super-symmetry. The ATLAS Muon Spectrometer (MS) is optimized to measure final state muons in a large momentum range, from a few GeV up to TeV. Its momentum resolution varies from (2-3%) at 10-100 GeV/c to 11% at 1 TeV, taking into account the high level background environment, the inhomogeneous magnetic field, and the large size of the apparatus (24 m diameter by 44 m length). A robust muon identification and high momentum measurement accuracy is crucial to fully exploit the physics potential of the LHC. The basic principles of the muon reconstruction packages Muonboy, STACO, MuTag are discussed in this paper. Details of the modifications done in order to adapt the pattern recognition to the cosmic-ray configuration as well as its performance with the recent cosmic-rays and single beam data are presented.
The 2004 H8 Testbeam setup is used as a test ground of various aspects of the ATLAS detector. The H8 study program focuses on sub-detector and trigger system performance in combined and standalone ...mode, as well as offline reconstruction and analysis, but leaves also space for specialized studies and experimental setups. In a dedicated setup, a BIS type Monitored Drift Tube chamber was placed in front of the Liquid Argon Calorimeter and was attached to its support structure. The aim of this project is to perform positioning measurements of the Liquid Argon Calorimeter electrodes using the track information from the BIS muon chamber. Moreover, the goal is to study the performance of the chamber in positron and muon beams at different beam incident angles. Last but not least, we investigate the correlation between the position of the cluster barycenter in the Liquid Argon and the reconstructed track in the BIS chamber.
The production of single- and multi-photon events has been studied in the reaction e(+) e(-) --> gamma(gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 ...and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.
We determined the prevalence of overweight and obesity in young Greek men in 2006 and examined variations related to their place of residence and educational level. Body height and weight were ...measured in 2568 conscripts of the Greek army, aged 19-26 years. The calculated body mass index (BMI, kg m⁻²) was correlated to their socio-demographic characteristics, i.e. level of education and place of residence (urban or rural). Overweight and obesity were defined according to the World Health Organization classification. Mean BMI (standard deviation) of the conscripts was 24.7 (4.2). The prevalence of overweight (30 > BMI >= 25 kg m⁻²) was 28.5% and correlated positively with a higher educational level, whereas the prevalence of obesity (BMI >= 30 kg m⁻²) was 10.4% and correlated positively with a lower educational level. Our data were compared with those of similar studies performed in the years 1969: BMI 23.8 (1.4) (P < 0.0001) and 1990: BMI 23.8 (2.9) (P < 0.0001), showing a positive secular trend for BMI in Greek conscripts in the last 16 years. In conclusion, we documented an alarmingly high prevalence of overweight and obesity among young Greek men.
A robust muon identification and high momentum measurement accuracy is crucial to fully exploit the physics potential that will be accessible with the ATLAS experiment at the LHC at CERN.
In this ...paper an overview of the muon reconstruction software is given and performance results from detailed Geant4-based simulations are presented.
A search for the Higgs boson has been performed in the H->WW->lvlv channel (l=e/mu) with an integrated luminosity of 2.05/fb of pp collisions at sqrt{s} = 7 TeV collected with the ATLAS detector at ...the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 110
A search for the Standard Model Higgs boson has been performed in the H->WW->lnujj channel using 4.7 fb^-1 of pp collision data recorded at a centre-of-mass energy of sqrt(s) = 7 TeV with the ATLAS ...detector at the Large Hadron Collider. Higgs boson candidates produced in association with zero, one or two jets are included in the analysis to maximize the acceptance for both gluon fusion and weak boson fusion Higgs boson production processes. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 300 GeV < mH < 600 GeV. The best sensitivity is reached for mH = 400 GeV, where the observed (expected) 95% confidence level upper bound on the cross section for H->WW produced in association with zero or one jet is 2.2 pb (1.9 pb), corresponding to 1.9 (1.6) times the Standard Model prediction. In the Higgs boson plus two jets channel, which is more sensitive to the weak boson fusion process, the observed (expected) 95% confidence level upper bound on the cross section for H->WW production with mH = 400 GeV is 0.7 pb (0.6 pb), corresponding to 7.9 (6.5) times the Standard Model prediction.
This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The ...asymmetry is measured in the W→μν decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb−1. The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.
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