Standalone vertex finding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to b bbar final states, and pp collision data at $\sqrt{s}$ = 7 TeV collected with the ATLAS detector at the LHC during 2011.
28 November 2013
Contact: PERF conveners
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Figures
Figure 01
Cross-sectional view of ATLAS in the r--z projection at φ = {π}/2. The barrel MDT chambers are shown in green, the endcap MDT chambers are blue. In the barrel (endcaps), the RPC (TGC) chambers are shown outlined in black (solid purple).
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Figure 02
Cross-sectional view of the barrel muon spectrometer perpendicular to the beam axis (non-bending plane). The MDT chambers in the small sectors are shown in light blue, the MDT chambers in the large sectors are shown in orange and the RPC chambers in red. The eight coils are also visible.
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Figure 03
Portion of a muon spectrometer barrel chamber (BIL) with two four-layer multilayers. The drift circles are shown in dark gray and the charged particle trajectory is shown as the black line. The spacing between the two multilayers is 170 mm.
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Figure 04
The probability for a π{v} to decay inside the fiducial volume of the muon spectrometer as a function of the π{v} mean proper lifetime (cτ).
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Figure 05
Transverse momentum (p{T}) distributions for charged particles from π{v} decays, at generator level.
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Figure 12
The average number of tracklets with a charge and momentum measurement reconstructed as a function of the position, in φ, of the displaced decay, for decays occurring in the barrel MS. All sectors have been projected such that the centre of a large sector corresponds to φ = 0 and the centre of a small sector corresponds to φ = ±{π}/8.
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Figure 17
Diagram illustrating the reconstruction technique employed in the barrel muon spectrometer. The display shows the simulated decay of a π{v} from the MC mass point mH = 140 GeV, mπ{v} = 20 GeV.
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Figure 22
Diagram illustrating the reconstruction technique employed in the endcap muon spectrometer. The display shows the simulated decay of a π{v} from the MC mass point mH = 140 GeV, mπ{v} = 20 GeV.
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Figure 27
Efficiency for reconstructing a vertex for π{v} decaying in the endcap MS as a function of the absolute z position of the π{v} decay.
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Figure 30
Distribution of the position, in (r,z), of all good vertices in the fiducial volume of the muon spectrometer in events that passed the barrel Muon RoI Cluster trigger from 1.94 fb-1 of 7 TeV pp collision data.
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Figure 31
The scale factor calculated by dividing the fraction of punch-through jets in data that have a good MS barrel vertex by the fraction in Monte Carlo simulation. The scale factor is calculated as a function of the number of MDT hits inside a cone of size Δ R = 0.6, centred around the jet axis.
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