Search

The Standard Model has been successful in describing many fundamental aspects of particle physics. However, there are some remaining puzzles which are not explained within the context of its present framework. We discuss the possibility to discover new physics in the ATLAS Detector via a four-fermion contact interaction, much in the same way Fermi first described Weak interactions. Using a simple ratio method, we find that we can set a 95% C.L. lower limit on the effective scale Lambda = 7.5 TeV (8.7 TeV) for the constructive Left-left Isoscalar Model of quark compositeness with 100 pb^-1 (200 pb^-1) of data at sqrt(s) = 10 TeV in the dimuon final state.

The Muon Spectrometer for the ATLAS experiment at the LHC is designed to identify muons with transverse momentum greater than 3 GeV/c and measure muon momenta with high precision up to the highest momenta expected at the LHC. The 50-micron sagitta resolution translates into a transverse momentum resolution of 10% for muon transverse momenta of 1 TeV/c. The design resolution requires an accurate control of the positions of the muon detectors and of the distortions of the nominal layout of individual chambers, induced by mechanical stress and thermal gradients during the experiment operation. Accurate calibration of the time to distance relation in the Monitored Drift Tubes is also required to reach design performance. We describe the software chain that implements corrections for the alignment and calibration of the chambers, as well as the algorithms implemented to perform pattern recognition and track fitting in the ATLAS Muon Spectrometer. In particular, we report on the performance of the complete software chain in the context of first single-beam LHC running as well as ATLAS combined cosmics data taking.

The Atlas Muon Spectrometer is designed to reach a very high transverse momentum resolution for muons in a pT range extending from 6 GeV/c up to 1 Tev/c. The most demanding design goal is an overall uncertainty of 50 microns on the sagitta of a muon with pT = 1 TeV/c. Such precision requires an accurate control of the positions of the muon detectors and of their movements during the experiment operation. Moreover, the light structure of the Muon Spectrometer, consisting mainly of drift tubes assembled in three layers of stations, imply sizable distortions of the nominal layout of individual chambers, due to mechanical stress and thermal gradients. Corrections for mis-alignments and deformations, which will be provided run-time by an optical alignment system, must be integrated in the software chain leading to track reconstruction and momentum measurement. Here we discuss the implementation of run-time dependent corrections for alignment and distortions in the detector description of the Muon Spectrometer along with the strategies for studying such effects in dedicated simulations. Some preliminary results obtained in the context of the ATLAS Condition Data Challenge effort are also presented.

The Muon Spectrometer for the Atlas experiment at the LHC is designed to identify muons with transverse momentum greater than 3 GeV/c and measure muon momenta with high precision up to the highest momenta expected at the LHC. The 50-micron sagitta resolution translates into a transverse momentum resolution of 10% for muon transverse momenta of 1 TeV/c. Precise tracking is provided by Monitored Drift Tubes at central and forward rapidities and by Cathode Strip Chambers at very forward rapidities. Dedicated alignment systems are a critical component of the design to attain such precision. We review the design of the muon reconstruction software and discuss the different pattern recognition approaches that have been developed. Track fitting and the handling of the inert material are also presented. The pattern recognition algorithms are required to be fast and efficienct for use in the high-level trigger, and they have been designed to take advantage of the characteristics of the signals from the different detector technologies in the spectrometer. Finally, we present the dedicated algorithms for cosmic-ray muon pattern recognition as well as first results from cosmic-ray data taking with the first muon chambers to be installed in the Atlas cavern.

The ATLAS detector, currently being installed at CERN, is designed to make precise measurements of 14 TeV proton-proton collisions at the LHC, starting in 2007. Arguably the clearest signatures for new physics, including the Higgs Boson and supersymmetry, will involve the production of isolated final-stated muons. The identification and precise reconstruction of muons are performed using a combination of detector components, including an inner detector, comprising a silicon tracker, pixel detector, and transition radiation tracker, housed in a uniform solenoidal field, and a precision muon spectrometer, comprising monitored drift tubes and cathode strip chambers, triggered by resistive plate chambers and thin-gap chambers, and housed in a toroidal field. We present current cross-detector reconstruction techniques used to exploit the strengths of the various detector components to best identify and measure muons in ATLAS, depending on their momentum and rapidity. Studies based on fully simulated GEANT4 events, using the complete detailed geometrical description of the detector are shown. We discuss recent developments in the combination of inner detector, muon spectrometer and calorimeter measurements, as well as developments in low transverse momentum muon identification. Preparations for LHC turn-on in 2007, including commissioning studies with cosmic rays and beam halo, are also discussed.