2,477 research outputs found
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
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
Optimisation of the Read-out Electronics of Muon Drift-Tube Chambers for Very High Background Rates at HL-LHC and Future Colliders
In the ATLAS Muon Spectrometer, Monitored Drift Tube (MDT) chambers and sMDT
chambers with half of the tube diameter of the MDTs are used for precision muon
track reconstruction. The sMDT chambers are designed for operation at high
counting rates due to neutron and gamma background irradiation expected for the
HL-LHC and future hadron colliders. The existing MDT read-out electronics uses
bipolar signal shaping which causes an undershoot of opposite polarity and same
charge after a signal pulse. At high counting rates and short electronics dead
time used for the sMDTs, signal pulses pile up on the undershoot of preceding
background pulses leading to a reduction of the signal amplitude and a jitter
in the drift time measurement and, therefore, to a degradation of drift tube
efficiency and spatial resolution. In order to further increase the rate
capability of sMDT tubes, baseline restoration can be used in the read-out
electronics to suppress the pile-up effects. A discrete bipolar shaping circuit
with baseline restoration has been developed and used for reading out sMDT
tubes under irradiation with a 24 MBq 90Sr source. The measurements results
show a substantial improvement of the performance of the sMDT tubes at high
counting rates
Performance of Drift-Tube Detectors at High Counting Rates for High-Luminosity LHC Upgrades
The performance of pressurized drift-tube detectors at very high background
rates has been studied at the Gamma Irradiation Facility (GIF) at CERN and in
an intense 20 MeV proton beam at the Munich Van-der-Graaf tandem accelerator
for applications in large-area precision muon tracking at high-luminosity
upgrades of the Large Hadron Collider (LHC). The ATLAS muon drifttube (MDT)
chambers with 30 mm tube diameter have been designed to cope with and neutron
background hit rates of up to 500 Hz/square cm. Background rates of up to 14
kHz/square cm are expected at LHC upgrades. The test results with standard MDT
readout electronics show that the reduction of the drift-tube diameter to 15
mm, while leaving the operating parameters unchanged, vastly increases the rate
capability well beyond the requirements. The development of new small-diameter
muon drift-tube (sMDT) chambers for LHC upgrades is completed. Further
improvements of tracking efficiency and spatial resolution at high counting
rates will be achieved with upgraded readout electronics employing improved
signal shaping for high counting rates
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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