1 / 17

Muon Performance of the ATLAS Detector in tt decays

T.Alexopoulos, M.Bachtis , G.Tsipolitis, G.Voutsinas National Technical University of Athens. Muon Performance of the ATLAS Detector in tt decays. Introduction. Muon performance study using muons from ttbar decays Muon (lepton) performance is important for Top Physics

alena
Download Presentation

Muon Performance of the ATLAS Detector in tt decays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. T.Alexopoulos, M.Bachtis, G.Tsipolitis, G.Voutsinas National Technical University of Athens Muon Performance of the ATLAS Detector in tt decays

  2. M. Bachtis - NTUA Introduction Muon performance study using muons from ttbar decays Muon (lepton) performance is important for Top Physics Mass measurement (dilepton decay channel) Jet Energy corrections Signal Identification A top MC sample was studied in the last version of Atlas software (300K events) Performance measurements Reconstruction Efficiency Pt ,η,φ resolution Isolation Comparison of Reconstruction algorithms Leptonic Top ν Hadronic Top

  3. M. Bachtis - NTUA ATLAS Detector INNER DETECTOR • Silicon pixels • Silicon strips • Transition radiation tracker • Solenoid Magnet EM CALORIMETER • Lead Plates as absorbers • Liquid argon as active medium MUON SPECTROMETER • Air core toroid magnets • Trigger and precision chambers cover all outer parts of ATLAS (Monitored Drift tube chambers), (Cathode Strip Chambers), (Resistive Plate Chambers), (Thin gap Chambers). HADRONIC CALORIMETER • Iron absorber with plastic Scintillating tiles (Central region) • Cooper/Tungsten absorber with LAr in forward regions

  4. M. Bachtis - NTUA ATLAS Muon Spectrometer Precision Chambers Monitored Drift Tube Chambers (1194) Barrel, EndCap Tube resolution = 80μm Cathode Strip Chambers (32) Endcap / small wheel Layer resolution = 60μm Trigger Chambers Resistive Plate Chambers (596) Barrel Trigger Thin Gap Chambers (4256) EndCap Trigger

  5. M. Bachtis - NTUA ATLAS Coordinate System

  6. M. Bachtis - NTUA Method Description Muons have a mean (true) Pt value of 50GeV Reconstructed Muons are compared to Monte Carlo tracks Two different reconstruction packages are tested MUID/MOORE (C++) STACO/MUONBOY (Fortran) Standalone Performance Muon Tracks + dE/dx Pt corrections in the Calorimeter Combined Performance Muon Spectrometer + Tracker Misaligned Geometry

  7. M. Bachtis - NTUA Simulated Top decay event with Muon

  8. M. Bachtis - NTUA Standalone & combined performance (MUID) Standalone Combined • Tracker dominates in the Pt measurement for the ~50 GeV Pt spectrum – Muon spectrometer is used for identification • But Muon spectrometer can also work standalone! • Tracker is needed for η,φ measurements • Geometrical Inefficiencies • Central gap (η=0) • Barrel – endcap boundary (η=+1,-1) • Detector feet -φ~ -1, -2 radians. • Stable efficiency vs Pt • Less efficiency for combined reconstruction • ( match of the ID track and the muon extrapolated track) [MeV] [rad] [rad]

  9. M. Bachtis - NTUA Geometrical Acceptance of the muon system

  10. M. Bachtis - NTUA Muon Spectrometer low acceptance regions Barrel – Endcap Transition region Central Gap Detector Feet

  11. M. Bachtis - NTUA Combined Performance Comparison MUID / Moore STACO / Muonboy • STACO more efficient than MUID for combined performance • Same resolution (~2.7%) [MeV] [rad] [rad]

  12. M. Bachtis - NTUA Standalone comparison MUID / Moore STACO/Muonboy • STACO/Muonboy more efficient than MUID/Moore for standalone performance • Same resolution (~4.1%) • Shift on the Pt resolution peaks [MeV] [rad] [rad]

  13. M. Bachtis - NTUA Shift in Pt Resolution • The Pt resolution distributions are shifted. • Difference by 0.5% • MUID/Moore is more centered

  14. M. Bachtis - NTUA Calorimeter Energy loss performance MUID / Moore Peaks for both Algorithms STACO/Muonboy • The are peaks at ~6GeV in the Eloss distribution for both algorithms • Geometrical effect • Peaks in the Eloss vs eta distribution for η=1, η=-1 (muons loose more energy) • Muons face more material in this region (Barrel Endcap boundary-diagonal) • Et loss distributions are shifted • Pt corrections different for each algorithm [MeV] [MeV] [MeV]

  15. M. Bachtis - NTUA Muon Isolation • Isolation energy = Calorimeter Energy deposit in a cone around particle - Eloss

  16. M. Bachtis - NTUA Summary Results Moore /MUID Muonboy/STACO Reconstruction Efficiency 93.4% / 90.1% 93.7% / 92.0% Number of Fakes 0 / 0 0 / 0 Pt Resolution (standalone) 4.1% 4.1% φ Difference (standalone) 0.0047 0.0046 η Difference (standalone) 0.0045 0.0045 Pt Resolution (combined) 2.7% 2.8% φ Difference (combined) 0.0001 0.0001 η Difference (combined) 0.0005 0.0005

  17. M. Bachtis - NTUA Conclusion ATLAS provides very accurate tracking measurements for muons For tt decays (muon Pt ~ 50GeV) Muon spectrometer is used for identification Tracker AND/OR Muon spectrometer used for Pt measurement Tracker for η,φ measurements Both algorithms show nice performance

More Related