Search for the Standard Model Scalar Boson with the ATLAS detector

The experimental results of the search for the Standard Model Higgs boson with the ATLAS detector at the Large Hadron Collider are reported, based on a dataset of pp collision data with an integrated luminosity of up to 4.9 fb^-1 at sqrt{s}=7 TeV. The search combines several Higgs boson decay channels in a wide range of Higgs boson masses from 110 GeV to 600 GeV. A Standard Model Higgs boson is excluded at the 95% confidence level in the mass ranges from 110.0 GeV to 117.5 GeV, 118.5 GeV to 122.5 GeV, and 129 GeV to 539 GeV, while the range from 120 GeV to 555 GeV is expected to be excluded in the absence of a signal. The most significant excess of events is observed around 126 GeV with a local significance of 2.5sigma. The global probability for such an excess to occur in the full searched mass range is approximately 30%.Comment: 8 pages, 14 pages, Proceedings for Recontres de Moriond EW 201

Muon Identification at ATLAS and CMS

Muonic final states will provide clean signatures formany physics processes at the LHC. The two LHC experiments ATLAS and CMS will be able to identify muons with a high reconstruction efficiency above 96% and a high transverse momentum resolution better than 2% for transverse momenta below 400 GeV/c and about 10% at 1 TeV/c. The two experiments follow complentary concepts of muon detection. ATLAS has an instrumented air-toroid mangetic system serving as a stand-alone muon spectrometer. CMS relies on high bending power and momentum resolution in the inner detector, and uses an iron yoke to increase its magnetic field. The iron yoke is instrumented with chambers used for muon identification. Therefore, muon momenta can only be reconstructed with high precision by combining inner-detector information with the data from the muon chambers

Performance of a First-Level Muon Trigger with High Momentum Resolution Based on the ATLAS MDT Chambers for HL-LHC

Highly selective first-level triggers are essential to exploit the full physics potential of the ATLAS experiment at High-Luminosity LHC (HL-LHC). The concept for a new muon trigger stage using the precision monitored drift tube (MDT) chambers to significantly improve the selectivity of the first-level muon trigger is presented. It is based on fast track reconstruction in all three layers of the existing MDT chambers, made possible by an extension of the first-level trigger latency to six microseconds and a new MDT read-out electronics required for the higher overall trigger rates at the HL-LHC. Data from $pp$-collisions at $\sqrt{s} = 8\,\mathrm{TeV}$ is used to study the minimal muon transverse momentum resolution that can be obtained using the MDT precision chambers, and to estimate the resolution and efficiency of the MDT-based trigger. A resolution of better than $4.1\%$ is found in all sectors under study. With this resolution, a first-level trigger with a threshold of $18\,\mathrm{GeV}$ becomes fully efficient for muons with a transverse momentum above $24\,\mathrm{GeV}$ in the barrel, and above $20\,\mathrm{GeV}$ in the end-cap region.Comment: 6 pages, 11 figures; conference proceedings for IEEE NSS & MIC conference, San Diego, 201

Precision Muon Tracking Detectors for High-Energy Hadron Colliders

Small-diameter muon drift tube (sMDT) chambers with 15 mm tube diameter are a cost-effective technology for high-precision muon tracking over large areas at high background rates as expected at future high-energy hadron colliders including HL-LHC. The chamber design and construction procedures have been optimized for mass production and provide sense wire positioning accuracy of better than 10 ?m. The rate capability of the sMDT chambers has been extensively tested at the CERN Gamma Irradiation Facility. It exceeds the one of the ATLAS muon drift tube (MDT) chambers, which are operated at unprecedentedly high background rates of neutrons and gamma-rays, by an order of magnitude, which is sufficient for almost the whole muon detector acceptance at FCC-hh at maximum luminosity. sMDT operational and construction experience exists from ATLAS muon spectrometer upgrades which are in progress or under preparation for LHC Phase 1 and 2

Construction and Test of New Precision Drift-Tube Chambers for the ATLAS Muon Spectrometer

ATLAS muon detector upgrades aim for increased acceptance for muon triggering and precision tracking and for improved rate capability of the muon chambers in the high-background regions of the detector with increasing LHC luminosity. The small-diameter Muon Drift Tube (sMDT) chambers have been developed for these purposes. With half of the drift-tube diameter of the MDT chambers and otherwise unchanged operating parameters, sMDT chambers share the advantages of the MDTs, but have an order of magnitude higher rate capability and can be installed in detector regions where MDT chambers do not fit in. The chamber assembly methods have been optimized for mass production, minimizing construction time and personnel. Sense wire positioning accuracies of 5 ?micons have been achieved in serial production for large-size chambers comprising several hundred drift tubes. The construction of new sMDT chambers for installation in the 2016/17 winter shutdown of the LHC and the design of sMDT chambers in combination with new RPC trigger chambers for replacement of the inner layer of the barrel muon spectrometer are in progress

Precision Muon Tracking at Future Hadron Colliders with sMDT Chambers

Small-diameter muon drift tube (sMDT) chambers are a cost-effective technology for high-precision muon tracking. The rate capability of the sMDT chambers has been extensively tested at the Gamma Irradiation Facility at CERN in view of expected rates at future high-energy hadron colliders. Results show that it fulfills the requirements over most of the acceptance of muon detectors. The optimization of the read-out electronics to further increase the rate capability of the detectors is discussed. Chambers of this type are under construction for upgrades of the muon spectrometer of the ATLAS detector at high LHC luminosities. Design and construction procedures have been optimized for mass production while providing a precision of better than 10 micrometers in the sense wire positions and the mechanical stability required to cover large areas.Comment: 5 pages, 12 figures; conference proceedings for IEEE NSS & MIC conference, San Diego, 201

Commissioning of the Charged Lepton Identification with Cosmic Rays in ATLAS

Efficient identification of charged leptons will be a key to the study of many physics processes at the Large Hadron Collider (LHC). The ATLAS detector at the LHC has excellent charged lepton identification capabilities. In the years 2008 and 2009, 300 million cosmic ray events were recorded by the ATLAS detector. These data were used to fully commissioning the muon identification algorithms, to prove the power of the electron identification algorithm and to partially commissioning the tau lepton identification

Precision Drift Chambers for the Atlas Muon Spectrometer

ATLAS is a detector under construction to explore the physics at the Large Hadron Collider at CERN. It has a muon spectrometer with an excellent momentum resolution of 3-10%, provided by three layers of precision monitored-drift-tube chambers in a toroidal magnetic field. A single drift tube measures a track point with a mean resolution close to 100 micron, even at the expected high neutron and gamma background rates. The tubes are positioned within the chamber with an accuracy of 20 microns, achieved by elaborate construction and assembly monitoring procedures.Comment: 3 pages, 2 eps figures, Proceedings for poster at Physics in Collisions Conference (PIC03), Zeuthen, Germany, June 2003. FRAP1

Large-Scale Production of Monitored Drift Tube Chambers for the ATLAS Muon Spectrometer

Precision drift tube chambers with a sense wire positioning accuracy of better than 20 microns are under construction for the ATLAS muon spectrometer. 70% of the 88 large chambers for the outermost layer of the central part of the spectrometer have been assembled. Measurements during chamber construction of the positions of the sense wires and of the sensors for the optical alignment monitoring system demonstrate that the requirements for the mechanical precision of the chambers are fulfilled