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Thijs Cornelissen (INFN Genova ) On behalf of the ATLAS collaboration

Muon reconstruction performance in ATLAS. Thijs Cornelissen (INFN Genova ) On behalf of the ATLAS collaboration. Outline. The ATLAS detector Muon performance with cosmics Muon performance with collision events. The Inner Detector (or inner tracker).

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Thijs Cornelissen (INFN Genova ) On behalf of the ATLAS collaboration

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  1. Muon reconstruction performance in ATLAS ThijsCornelissen (INFN Genova) On behalf of the ATLAS collaboration

  2. Outline • The ATLAS detector • Muon performance with cosmics • Muon performance with collision events

  3. The Inner Detector (or inner tracker) Immersed in a solenoid field of 2 Tesla measures the trajectories of charged particles. The ID comprises 3 sub-detectors: (resolution) Pixel : 10/115 μm in Rϕ/z Silicon strip (SCT): 17/580 μm Transition radiation tracker (TRT): 130 μm in Rϕ The ID covers : |η| < 2.5 (2.0 for TRT) with 3 Pixel measurements, 8 SCT and ~30 TRT. Designed for tracking efficiency >90% (p) and 99% (m) , momentum measurement with σpT /pT = 0.05% pT ⊕1% and impact parameter (at high p) = 10 mm

  4. The muon spectrometer • Immersed in a toroidal magnetic field of ~ 0.5 T (3x8 superconducting toroids) • Precision measurement chambers and trigger chambers • MDT (Monitored Drift Tubes) • RPC (Resistive Plate Ch.) • CSC (Cathode Strip Chambers) • TGC (Thin-Gap Chambers) • coverage |η|<2.7

  5. Muon reconstruction algorithms • Muons can be reconstructed in the inner detector (ID), the calorimeters, and/or the muon spectrometer (MS) • Several different types of reconstruction algorithms: • ‘Standalone’ muons are reconstructed in the MS, then extrapolated to the vertex • ‘Combined’ muons are produced by matching an ID track to a MS track, then either a full refit or a weighted average is performed • Gives best possible momentum resolution • ‘Tagged’ muons are ID tracks matched with one or more segments in the MS • Useful in particular if the momentum is insufficient to leave a full track in the MS • Initial studies focused on efficiencies and resolutions, using ~0.6 nb-1 recorded with the minimum bias trigger

  6. 2008 and 2009: cosmics studies

  7. Inner detector cosmics studies • Track parameter resolution studied by splitting cosmic track into upper and lower half, and comparing the parameters • Tracking efficiencies very high, as expected (muons) • Cosmics probe mainly barrel region, statistics in endcaps much lower

  8. Muon spectrometer cosmics studies Large sectors ATLAS preliminary Small sectors MDT residuals snarrow=98 mm ATLAS preliminary • Momentum resolution looks promising (better than ID for pT > 100 GeV) • Resolution studies using combined tracks ongoing

  9. Muons in 900 GeV run • Most particles in the 900 GeV run had low momentum, did not make it much further than the inner tracker. • Still, O(100) muon candidates recorded (mostly from pion/kaon decays), and even a couple of di-muon events

  10. Track parameter distributions combined muons Basic track parameter distributions show good agreement between data and simulation Simulation shows contributions from prompt muons (including b/c decays) in red, early p/K decays in green, late decays in white

  11. Number of hits on track combined muons 3 stations ATLAS preliminary ATLAS preliminary 2 stations Number of ID hits on track well described by simulation (see presentation by T. Kuhl) Good agreement between data and simulation concerning number of MDT and CSC hits on track

  12. First efficiency measurements • Reconstruction efficiencies estimated by comparing overlap between algorithms • Use tagged muons that are confirmed as calorimeter muons, check if combined algorithm found the muon • Efficiencies underestimated due to contamination of sample by p/K decays • Decays are often rejected by combined algorithms • Ultimately, efficiencies will be determined using tag&probe with resonances ATLAS preliminary

  13. Momentum resolution • Resolution of MS tracks studied by comparing momentum with ID track • Expected resolution ~5% for MS tracks, ~2.5% for ID tracks (on average) • Asymmetric tail due to p/K decays, larger in data than in simulation • Under investigation ATLAS preliminary

  14. Muon energy deposit and isolation Muons inside jets have much larger energy deposits around them Excellent data/MC agreement concerning energy deposits Simulation can thus be used to optimize isolation cuts ATLAS preliminary ATLAS preliminary Calorimeter isolation Track isolation ATLAS preliminary

  15. Conclusions • First 0.6 nb-1 has been used to assess the performance of the ATLAS muon reconstruction • Relative efficiency measurements, muon isolation studies show very good data/MC agreement • Now working towards full program using J/Ys and Zs

  16. Backup

  17. Composition in MC truth ATLAS preliminary

  18. State of ATLAS for first 7 TeV collisions Muon EE chambers (|h|~1.2) not yet installed

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