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Abstract: The ATLAS muon spectrometer consists of a system of precision tracking and trigger chambers embedded in a 2T magnetic field generated by three large aircore superconducting toroids. The precision Monitored Drift Tube (MDT) chambers measure the track sagitta up to a pseudorapidity of 2.7 with a 50 μm uncertainty yielding a design muon transverse momentum resolution of 10% at 1 TeV. Muon tracking is augmented in the very forward region by Cathode Strip Chambers (CSC). The calibration program, essential to achieve the spectrometer design performance and physics reach, is conducted at three worldwide computing centers. These centers each receive a dedicated High Level Trigger data stream that enables high statistics based determination of t0 and drifttime to driftspace relations. During the first year of data taking a system of periodic calibration updates has been established. The calibration algorithms, methods and tools and performance results using LHC collision data are discussed. [Copyright &y& Elsevier]

Abstract: Monitored drift tube chambers are used as precision tracking detectors in the muon spectrometer of the ATLAS experiment at the LHC at CERN. These chambers provide a spatial resolution of 35μm and a tracking efficiency of close to 100% up to background rates of 0.5kHz/cm2, the former being limited at higher rates mainly due to space-charge effects and the latter due to the maximum drift time of 700ns. For LHC upgrades, a faster drift tube chamber has been developed, using drift tubes with a diameter of 15mm instead of 30mm. The increased channel density and shorter drift time of about 200ns raise the rate capability to about 10kHz/cm2, while retaining the spatial resolution. A prototype chamber with trapezoidal shape consisting of 2 x 8 layers of 15mm diameter drift tubes with an active surface of 0.8 m2 has been constructed. The prototype chamber has been tested at CERN with a 180GeV muon beam at a SPS beam line and with cosmic ray muons at the Gamma Irradiation Facility (GIF) at high γ radiation rates. [Copyright &y& Elsevier]

Abstract: The ATLAS iron-scintillator hadronic calorimeter (TileCal) provides precision measurements of jets and missing transverse energy produced in the LHC proton-proton collisions. Results assessing the calorimeter calibration obtained using cosmic ray muons collected in 2008, 2009 and 2010 are presented. The analysis was based on the comparison between experimental and simulated data, and addresses three issues. First the average non-uniformity of the response of the cells within a layer was estimated to be about ±2%. Second, the average response of different layers was found to be not inter-calibrated, considering the sources of error. The largest difference between the responses of two layers was 4%. Finally, the differences between the energy scales of each layer obtained in this analysis and the value set at test beams using electrons was found to range between -3% and +1%. The sources of uncertainties in the response measurements were strongly correlated, including the uncertainty in the simulation. The total error of each layer determinations was 2%. Stable response values were obtained for the three data-taking periods. The uncertainties on the comparisons were less than ±1% for the Long Barrel layers and less than ±3% for the Extended Barrel ones. [Copyright &y& Elsevier]

Abstract: The ATLAS muon spectrometer is designed to measure the momentum of a 1 TeV/c muon to an accuracy of 10%. A muon of this momentum bends, on average, 500μm in the toroidal field of ATLAS. Therefore, the position of the muon chambers within a tower and along the precision coordinate must be known to better than 50μm. ATLAS uses a combination of an optical and track-based alignment to achieve such a precise alignment. Several analyses to monitor and validate the alignment were undertaken in the first year of LHC operation. This report provides a brief overview of the motivation, building and commissioning of the optical system, performance, and validation of the alignment of the muon spectrometer. [Copyright &y& Elsevier]

TileCal is the hadronic tile calorimeter of the ATLAS experiment at LHC/CERN. The central element of the back-end system of the TileCal detector is the Read-Out Driver (ROD).The main components of the TileCal ROD are the Digital Signal Processors (DSPs) placed on the Processing Unit (PU) daughterboards. This paper presents a detailed description of the code developed for the DSPs. The code is divided into two different parts: the first part contains the core functionalities and the second part the reconstruction algorithms. The core acts as an operating system and controls configuration, data reception and transmission and synchronization between front-end data and the Timing, Trigger and Control (TTC) information. The reconstruction algorithms implemented on the DSP are the Optimal Filtering (OF), Muon Tagging (MTag) and Missing ET calculation. The OF algorithm reconstructs the deposited energy and the phase of the signal for every calorimeter channel within a front-end module. This reconstructed energy is used by the MTag algorithm to tag low transverse momentum muons that may escape the ATLAS muon spectrometer Level 1 trigger whereas the Missing ET algorithm computes the total transverse energy and the projection on X and Y axis for the entire module that will be used by the Level 2 trigger system. [ABSTRACT FROM AUTHOR]

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of selecting interesting candidate events in proton-proton collisions at 14 TeV center of mass energy, while rejecting the enormous number of background events. The trigger system architecture is organized in three levels. From a bunch crossing rate of 40 MHz, the First Level trigger, hardware implemented, will reduce this rate to around ∼ 75 kHz. Then the software based High Level Trigger (HLT), composed by the Second Level Trigger and the Event Filter reduces the rate to ∼ 200 Hz. In this paper, we will present the implementation of the muon trigger "slice," signal efficiencies, background rejection rates, and system performances (execution time, memory consumption, etc.) for online muon selection based on Monte Carlo simulations and results obtained on real events collected during cosmic data taking runs. [ABSTRACT FROM AUTHOR]

The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. A three-level trigger system will select potentially interesting events in order to reduce the read-out rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 104 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level central trigger and the muon barrel trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware. [ABSTRACT FROM AUTHOR]