Muons in ATLAS

1. Muons in ATLAS Alexander Oh University of Manchester on behalf of the ATLAS Collaboration ATL-COM-MUON-2010-024

2. Muons • Detector and Reconstruction • Alignment and Calibration status • Trigger Performance • Reconstruction Performance Alexander Oh (Manchester University) - ATLAS Collaboration

3. Detector: Muon Spectrometer • Fast trigger chambers: • Resistive Plate Chambers (barrel) • Thin Gap Chambers (end-caps) • Precision chambers: • Monitored Drift Tubes (barrel and end-cap) • Cathode Strip Chambers (forward region 2.0 < eta < 2.7) • Toroidal magnetic field of 0.5 T • barrel and two end-cap toroids • 8 fold geometry • complex field Alexander Oh (Manchester University) - ATLAS Collaboration

4. Detector: Inner Detector • Silicon Tracker • Pixels (3 layers) • Strips (4 barrel layers, 9 end-cap layers) • Coverage |eta| < 2.5 • Transition Radiation Tracker • Coverage |eta| < 2.0 • Solenoidal magnetic field of 2.0 T Alexander Oh (Manchester University) - ATLAS Collaboration

5. Muon Reconstruction Objective: Muon identification in a wide momentum range from GeV (Onia) to TeV (BSM). Make use of all detector components and use different strategies: • Muon Spectrometer Standalone (MS) reconstruction • MS and Inner Detector (ID) combined fit • Outside-in • Inside-out • Statistical combination • Taggers • ID track is matched to MS segments • ID track is matched to a MIP in calorimeter Alexander Oh (Manchester University) - ATLAS Collaboration

6. Alignment and Calibration Status Alexander Oh (Manchester University) - ATLAS Collaboration

7. Alignment and Calibration Status: MS • Alignment • Optical alignment system • Barrel: relative • End-caps: absolute • Data with toroid B-field off. • Measure alignment with straight tracks. Cosmics data 2008 barrel alignment±50 mm (large sectors) ±100 mm (small sectors) end-cap alignment±45 mm Cosmics data 2008 Alexander Oh (Manchester University) - ATLAS Collaboration

8. Alignment and Calibration Status: ID • Track based alignment • First alignment with cosmics tracks. • First collisions at 900 GeV were used to improve the alignment. • Performance study with 7 GeV data. New alignment constant set in progress. Alexander Oh (Manchester University) - ATLAS Collaboration

9. Trigger Performance Alexander Oh (Manchester University) - ATLAS Collaboration

10. see also Ricardo Goncalo: Atlas Trigger Trigger • L1 custom hardware • Require coincidence in eta phi view. • pT estimation based on geometrical roads. • Road definition and time alignment commissioned. • HLT software • L2: Pattern recognition, LUT based pT estimate • EF: Full muon reconstruction available • L1, L2 and EF are commissioned and used for active rejection. TGC, timing optimization Alexander Oh (Manchester University) - ATLAS Collaboration

11. Trigger L1 efficiency, T&P with J/PsiBarrel + End-caps • Efficiency determined by looking at • Inclusive muons relative to offline. • Tag & Probe method on J/Psi and Z events. • Trigger Efficiencies at L1 • barrel 75% • end-cap 95% • Rel. Trigger efficiencies at HLT • L2 >98% • EF >98% L1 efficiency, inclusive muon Barrel EF efficiency, inclusive muonBarrel + End-caps Alexander Oh (Manchester University) - ATLAS Collaboration

12. Trigger • Muon rates measured in data. • Extrapolation to higher luminosity. • Determines evolution of trigger strategy. Allocated rate Alexander Oh (Manchester University) - ATLAS Collaboration

13. Reconstruction Performance Alexander Oh (Manchester University) - ATLAS Collaboration

14. Reconstruction Efficiency • Determination from Cosmics • Select events with ID tracks traversing MS barrel. • Look for MS track in • top hemisphere (pID > 5 GeV) • bottom hemisphere (pID > 9 GeV) • Measures reconstruction efficiency of MS conditional to a L1 trigger. ATLAS Preliminary 2009 Cosmic Data ATLAS Preliminary 2009 Cosmic Data Turn on curve:Good agreement between Data and MC Average efficiency: 97.4 ±0.1 % 95.2 ±0.1 % Alexander Oh (Manchester University) - ATLAS Collaboration

15. Reconstruction Efficiency • Relative Efficiency from Data • Use independent algorithms to assess reconstruction efficiency. • Combined algorithm efficiency estimated by comparing overlap to calorimeter and segment tag algorithms. • Tag and Confirm method with sample of J/Psi’s (purity ~98%) • Tag and Probe studies are under preparation with J/Psi and Z. Alexander Oh (Manchester University) - ATLAS Collaboration

16. (Non-)Prompt Muons Muons from light hadrons (“non-prompt”) • Decay within the ID volume • Hadron and the secondary muon are reconstructed as one track • momentum mismatch of ID and MS pt Muons from heavy flavour (“prompt”) • Secondary muon produced close to IP • ID and MS measure the muon track. Discriminate by “loss momentum” fraction between MS and ID pT measurement: Use templates derived from MC to determine fractions of “prompt” and “non-prompt” secondary muons. K0s -> p+p- ID barrel J/Y -> m+m- Alexander Oh (Manchester University) - ATLAS Collaboration

17. (Non-)Prompt Muons • Fraction of prompt muons determined in bins of pT and eta. • MC and data agree within uncertainties • Dominant systematic uncertainties: • template shape at low pT • MC flavor content at high pT ID end-cap ID barrel Alexander Oh (Manchester University) - ATLAS Collaboration

18. Momentum Scale and Resolution • Use MS and ID pT measurement to extract scale and resolution. • Disentangle “prompt” and “non-prompt” contribution. • Background template from QCD MC • Signal template: Gauss × Landau extract scale (xG) and resolution (sG+sL) Alexander Oh (Manchester University) - ATLAS Collaboration

19. Momentum Scale and Resolution Barrel region: Generally good agreement between data and MC. End-cap region: Due to alignment resolution in data worse then in MC. Alexander Oh (Manchester University) - ATLAS Collaboration

20. Summary & Outlook • Performance of detector, trigger and reconstruction studied with first data and cosmic events. • Good agreement between data and MC. • Presented results used only a fraction of the available data. • Many more results to come soon with the full data set! Alexander Oh (Manchester University) - ATLAS Collaboration

21. Backup Alexander Oh (Manchester University) - ATLAS Collaboration

22. Alignment and Calibration StatusMonitored Drift Tubes (MDT): Timing • Constant time offset t0 for each channel. • Leading edge of drift time spectrum. • Radius – drift time relation (rt) determined from auto-calibration method • Adjusted using residual distribution of track fit • More statistics needed for final calibration • t0 from track segment fitter • Resolution 20-50% worse than optimal − t0 refit − RPC timing− testbeam Alexander Oh (Manchester University) - ATLAS Collaboration

23. Fake Muons from pions • Determine fraction of p being reconstructed as m. • decay-in-flight • punch-through • High purity p sample from K0s -> p+p- • common vertex • transverse decay length [5 mm ,120 mm ] • p(p+p-) aligned with K0s flight direction • Purity ~95% • Probe: p ID track • p > 3 GeV • pT > 1 GeV • Tag: Muon candidate associated to the p ID track. identified m Alexander Oh (Manchester University) - ATLAS Collaboration

24. Fake Muons from pions • Fraction of fake muons extracted by fit to K0s mass spectrum. • Fake fraction • 0.101±0.014% (combined and tagged) • 0.070±0.012% (combined only) • Good agreement between data and MC Alexander Oh (Manchester University) - ATLAS Collaboration