Publications (14)0 Total impact
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Article: Non-SM Higgs Searches at the LHC
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ABSTRACT: We review the prospects for the Higgs boson searches in the Minimal Supersymmetric Standard Model (MSSM) with the ATLAS and CMS experiments at the Large Hadron Collider (LHC). In preparation for the approaching start of the LHC operation, the discovery reach accessible in proton-proton collisions at a center-of-mass energy of √(s) =14 TeV has been recently updated by both experiments. The results are interpreted within the mhmax benchmark scenario. -
Article: Study of the Higgs Discovery Potential in the Process pp->H->4$\mu$
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ABSTRACT: In this thesis we study the potential for the discovery of the Standard Model Higgs boson in the ATLAS detector in the decay channel \linebreak $H \to ZZ^{*} \to \mu^+ \mu^- \mu^+ \mu^-$. The ATLAS experiment at the Large Hadron Collider at CERN is designed to study the physics phenomena appearing in the proton-proton collisions at the 14~TeV center-of-mass energy. In the study of the physics processes involving muons in the final state an important role is played by the ATLAS muon spectrometer. The spectrometer allows for a precision muon momentum measurement independently of other ATLAS subdetectors. The performance of the spectrometer is greatly influenced by the performance of the muon tracking detectors, the Monitored Drift Tube Chambers (MDT). We perform the tests of the mechanical chamber accuracy, as well as the tests of the chamber response to muons. The mechanical accuracy of the chamber construction is shown to be well within the required 20~$\mu$m. The tests of the chamber response to muons show a spatial resolution of 100~$\mu$m in an individual drift tube of the chamber. This resolution can be improved to 80~$\mu$m using the final readout electronics. The efficiency of the muon detection in a drift tube is 93\%, which allows for an efficient muon track reconstruction in the spectrometer. The spatial resolution and the detection efficiency stay within the specifications even at the high photon background rates expected to appear in the spectrometer during the high luminosity running period. In addition to the chamber tests, we develope a precise method for the determination of the spatial resolution of the drift tube which is required for an efficient muon track reconstruction. The measured chamber properties are taken into account for the simulation of the $H \to ZZ^{*} \to \mu^+ \mu^- \mu^+ \mu^-$ process and of the corresponding background processes in the detector. We perform the optimization of the cuts for the background rejection in order to achieve the maximum signal significance. The obtained signal significance for the studied decay channel after three years of ATLAS operation at the low luminosity is between $s=2$ (for Higgs masses of 130 and 180~GeV/c$^2$) and $s=4$ (for a Higgs mass of about 150~GeV/c$^2$). -
Article: Studies of Semitransparent Optoelectronic Position Sensors (ALMY) for High Precision Alignment Monitoring Systems
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ABSTRACT: The deterioration of the sensitivity of amorphous silicon strip photo detectors ('ALMY' sensors) under long-term illumination has been studied with collimated laser beams of different wavelengths and intensities. The high position sensitivity of the ALMY sensors allows for the precise localization of the illumination point and for monitoring of the local sensitivity degradation with respect to the rest of the non-illuminated sensor area.Nuclear Instruments and Methods in Physics Research Section A, 568, 18-21 (2006). -
Article: Precision Drift Chambers for the Atlas Muon Spectrometer
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ABSTRACT: 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.Physics Letters B, 583, 87-95 (2004). -
Article: Development of Precision Muon Drift-Tube Detectors for the High-Luminosity Upgrade of the Large Hadron Collider
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ABSTRACT: For use at the future Super-LHC a new type of muon detector has been developed. It is based on the proven MDT drift tube design, but with tubes of half the diameter, leading to higher rate capabilities by an order of magnitude. We present test results on efficiency and position resolution at high background rates and describe the practical implementation in a real-size prototype. -
Article: Study of the Higgs Discovery Potential in the Process $pp \to H \to 4\mu$
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ABSTRACT: In this thesis we study the potential for the discovery of the Standard Model Higgs boson in the ATLAS detector in the decay channel \linebreak $H \to ZZ^{*} \to \mu^+ \mu^- \mu^+ \mu^-$. The ATLAS experiment at the Large Hadron Collider at CERN is designed to study the physics phenomena appearing in the proton-proton collisions at the 14~TeV center-of-mass energy. In the study of the physics processes involving muons in the final state an important role is played by the ATLAS muon spectrometer. The spectrometer allows for a precision muon momentum measurement independently of other ATLAS subdetectors. The performance of the spectrometer is greatly influenced by the performance of the muon tracking detectors, the Monitored Drift Tube Chambers (MDT). We perform the tests of the mechanical chamber accuracy, as well as the tests of the chamber response to muons. The mechanical accuracy of the chamber construction is shown to be well within the required 20~$\mu$m. The tests of the chamber response to muons show a spatial resolution of 100~$\mu$m in an individual drift tube of the chamber. This resolution can be improved to 80~$\mu$m using the final readout electronics. The efficiency of the muon detection in a drift tube is 93\%, which allows for an efficient muon track reconstruction in the spectrometer. The spatial resolution and the detection efficiency stay within the specifications even at the high photon background rates expected to appear in the spectrometer during the high luminosity running period. In addition to the chamber tests, we develope a precise method for the determination of the spatial resolution of the drift tube which is required for an efficient muon track reconstruction. The measured chamber properties are taken into account for the simulation of the $H \to ZZ^{*} \to \mu^+ \mu^- \mu^+ \mu^-$ process and of the corresponding background processes in the detector. We perform the optimization of the cuts for the background rejection in order to achieve the maximum signal significance. The obtained signal significance for the studied decay channel after three years of ATLAS operation at the low luminosity is between $s=2$ (for Higgs masses of 130 and 180~GeV/c$^2$) and $s=4$ (for a Higgs mass of about 150~GeV/c$^2$). -
Article: Upgrade of the ATLS Muon Trigger for the SLHC
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ABSTRACT: The outer shell of the ATLAS experiment at the LHC consists of a system of toroidal air-core magnets in order to allow for the precise measurement of the transverse momentum p$_T$ of muons, which in many physics channels are a signature of interesting physics processes. For the precise determination of the muon momentum Monitored Drift Tube chambers (MDT) with high position accuracy are used, while for the fast identification of muon tracks chambers with high time resolution are used, able to select muons above a predefined p$_T$ threshold for use in the first Level of the ATLAS triggering system (Level-1 trigger). When the luminosity of the LHC will be upgraded to 4-5 times the present nominal value (SLHC) in about a decade from now, an improvement of the selectivity of the ATLAS Level-1 triggering system will be mandatory in order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1 trigger of the ATLAS muon spectrometer this means an increase of the p$_T$ threshold for single muons. Due to the limited spatial resolution of the trigger chambers, however, the selectivity for tracks above ~20 GeV/c is insufficient for an effective reduction of the Level-1 rate. We describe how the track coordinates measured in the MDT precision chambers can be used to decisively improve the selectivity for high momentum tracks. The resulting increase in latency will also be discussed.Journal of Instrumentation, 5, C12016 (2010). -
Article: Prospects for data-driven estimation of the $\mu^+\mu^-$ background for neutral MSSM Higgs searches in the decay channel /H/A \to \mu^+\mu^-$
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ABSTRACT: This note describes the discovery prospects for the neutral MSSM Higgs bosons in the decay channel h/H/A->µ+µ- with the ATLAS detector. The analysis is performed for $\sqrt{s}$ = 10 TeV collision data simulated with full and fast simulation assuming Higgs masses of 130, 150 and 200 GeV and a benchmark point of $\tan{\beta}$ = 40. A good knowledge of the large Standard Model background, dominated by the Z and tt production, is crucial for the exclusion of the signal in early data analyses. Thus, a method is presented which allows to estimate these backgrounds from data by means of signal-free control samples from e+e- and eµ final states. The method is based on the vanishing decay rate h/H/A->e+e-. In contrast, the top quarks and Z bosons decay with equal probability into electrons and muons. Differences between the dielectron and dimuon final states arising from detector properties and photon radiation are studied in detail. The expected accuracy of the method is evaluated for different integrated luminosities of 0.2, 1 and 4 fb-1 by comparing the control samples with the actual µ+µ- background. Finally, the information from the control samples and the side band regions in the µ+µ- final state are combined to calculate the exclusion limits at a 95% confidence level. -
Article: Dependence of the Space-to-Drift-Time Relationship of Monitored Drift-Tube Chambers on the Magnetic Field in the ATLAS Muon Spectrometer
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ABSTRACT: The ATLAS detector is a multi-purpose detector which is built for the search for the standard model Higgs particle and new physics at the Large Hadron Collider (LHC). A striking feature of its design is the muon spectrometer, which is able to measure muon momenta with an accuracy of 3% over a wide momentum range; at 1 TeV/c an accuracy of 10% will be achieved. In the muon spectrometer, the muon trajectories will be measured by three stations of monitored drift-tube (MDT) chambers. The MDT chambers are operated in an average magnetic field of 0.4 T which is generated by 8 superconducting air-core toroid coils. The MDT chambers of the inner and outer layers in the barrel region are mounted outside the magnet coils and therefore experience a highly non-uniform magnetic field with field variations of up to 0.4 T. Due to the bending of the paths of the drift electrons in the magnetic field, the space-to-drift-time relationship r(t) depends on the magnetic field inside a tube. The maximum drift-time of 700 ns in absence of a magnetic field is extended by about 70 ns/T. The dependence of r(t) must be corrected for with an accuracy of 1 ns in order to achieve a chamber resolution of 50 $\mu$m. The dependence of r(t) on the magnitude and the orientation of the magnetic field with respect to the anode wires of the tubes and the muon incident angle was measured in a test-beam. These measurements allow for a parameterization of the magnetic-field dependence of r(t) with the required accuracy of 1 ns. -
Article: Test, Integration, Commissioning and Installation of Large Drift Tube Chambers of the ATLAS Barrel Muon Spectrometer
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ABSTRACT: The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is currently being assembled and to be ready to take data in 2007. In the barrel part of the muon spectrometer a toroidal air-core magnet is instrumented with three layers of Monitored Drift Tube (MDT) chambers as precision tracking detectors. The installation of the muon detectors has started in January 2005. At the Max-Planck-Institut f\"ur Physik and the Ludwig-Maximilians-University in Munich, 88 MDT chambers, each covering an area of 8 m$^{\text{2}}$, are being built for the outermost barrel region. The MDT chambers have to pass a series of stringent tests before installation to ensure their proper operation in the experiment. At the production site in Munich, these tests include gas tightness, high voltage stability and measurements of the noise rate, and the response to cosmic muons. In addition, the individual wire positions and electronic time offsets of the drift tubes are determined from the cosmic ray data. At CERN, a subset of the tests is repeated and the MDT chambers are integrated on a common support frame with Resistive Plate Chambers (RPCs) of the trigger system. The results of the tests are stored in the ATLAS commissioning database and form an important basis for LHC data taking. We present the test methods and results, an overview on the integration work of the muon detectors and report on the experience with their installation in the ATLAS experiment. -
Article: Modelling of the Space-to-Drift-Time Relationship of the ATLAS Monitored Drift-Tube Chambers in the Presence of Magnetic Fields
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ABSTRACT: The ATLAS muon spectrometer uses tracking chambers consisting of up to 6 m long drift tubes filled with Ar:CO2 (93:7) at 3 bars. The chambers are run in a average toroidal magnetic field of 0.4 T created by 8 air core coils. They provide a track point accuracy of 40 µm if the space-to-drift-time relationship r(t) is known with 20 µm accuracy. The magnetic field B influences the electron drift inside the tubes: the maximum drift time tmax=700 ns increases by about 70 (ns/T^2)*B^2 . B varies by up to ±0.4 T along the tubes of the chambers mounted near the magnet coils which translates into a variation of tmax of up to 45 ns. The dependence of r(t) on B must be taken into account. Test-beam measurements show that the electron drift in case of B>0 can be modelled with the required accuracy by a Langevin equation with a friction term which is slightly non-linear in the drift velocity. -
Article: Test, Integration and Commissioning of Monitored Drift Tube Chambers for the ATLAS Barrel Muon Spectrometer
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ABSTRACT: The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is currently being assembled and to be ready for data taking in 2007. In the barrel region of its muon spectrometer, a toroidal air-core magnet is instrumented with three layers of Monitored Drift Tube (MDT) chambers as precision tracking detectors; the middle and outer layers of drift chambers also carry Resistive Plate chambers (RPCs) of the trigger system. The barrel part of the spectrometer consists of a total of 682 muon stations, with sizes ranging from 1~m$^{2}$ to 11~m$^{2}$. The installation of the muon detectors has started in January 2005. At the Max-Planck-Institut f\"ur Physik and theLudwig-Maximilians-University in Munich, 88 MDTs of the second largest chamber type---each covering an area of up to 8~m$^{2}$---are being built for the outermost barrel region. The MDT chambers have to pass a series of stringent tests before installation to ensure their proper operation in the experiment. At the production site in Munich, these tests include gas tightness, high voltage stability and measurements of the noise rate, and the response to cosmic muons. In addition, the individual wire positions and electronic time offsets of the drift tubes are determined from the cosmic ray data. After shipment to CERN, a subset of the tests is repeated and the MDT chambers are integrated on a common support frame with the trigger chambers. The completed muon station is further checked with cosmic rays. All results are stored in the ATLAS commissioning database and constitute an important basis for LHC data taking. We present the test methods and results, an overview on the integration work of the muon detectors and report on the experience with the installation of the first stations in the ATLAS experiment. -
Article: Test, Integration and Commissioning of Monitored Drift Tube Chambers for the ATLAS Barrel Muon Spectrometer
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Article: Study of the long-terlll behavior of the sensitivity of alllorphous silicon photo detectors under illulllination
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ABSTRACT: The deterioration of the sensitivity of amorphous silicon strip photo detectors (' ALMY' sensors) under long-term illumination has been studied with collimated laser beams of different wavelengths and intensities. The high position sensitivity of the ALMY sensors allows for the precise localization of the illumination point and for monitoring of the local sensitivity degradation with respect to the rest of the non-illuminated sensor area.
