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Performance of the ATLAS muon spectrometer

Performance of the ATLAS muon spectrometer . Marcello Bindi , on behalf of ATLAS Collaboration. KRUGER 2010 : Workshop on Discovery Physics at the LHC . ATLAS Muon Spectrometer. y. Three large super-conducting air-core toroidal magnets (2~6 T· m) Weight : 7000 tons. z. x.

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Performance of the ATLAS muon spectrometer

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  1. Performance of the ATLAS muon spectrometer Marcello Bindi, on behalf of ATLAS Collaboration KRUGER 2010:Workshop on Discovery Physics at the LHC

  2. ATLAS Muon Spectrometer y Three large super-conducting air-core toroidal magnets (2~6 T·m) Weight : 7000 tons z x 25 meter of diameter, 44 meter length including also the End-caps Marcello Bindi - University and INFN of Bologna - Kruger2010

  3. Muons for ATLAS physics Muon : promising probe for new physics - clean signature of final states with muons over largest possible solid angle is crucial for physics at LHC - HZZ*μμll, A μμ, Z’μμ… - required mass resolution: Δm/m < few % H ZZ* μ+μ−μ+μ− Challenging issues for Muon Spectrometer • Trigger Selectivity: – select muons (pT > 6 GeV) from interaction point • – identify interesting events with 25 ns accuracy • PT resolution:3~4% up to pT = 100 GeV, 10% for pT ~ TeV. • Charge identification for pT ~ TeV. Marcello Bindi - University and INFN of Bologna - Kruger2010

  4. p ~ p ~ Marcello Bindi - University and INFN of Bologna - Kruger2010

  5. 4detectorswithdifferentpurposes Precise spatial measurements Trigger and Readout Resistive Plate Chambers RPC (barrel) | η | < 1.1, 360k ch, 6 layers Monitored drift tubes MDT (barrel + end-cap) |η| < 2.7, 370k ch, 6 multi layer Thin Gap Chambers TGC (end-cap) 1.1 < | η | < 2.4, 440k ch, 7 layers Cathodes Strip Chambers CSC (forward) 2.0 < | η | < 2.7, 31k ch, 4 layers Marcello Bindi - University and INFN of Bologna - Kruger2010

  6. Muon detectors and the B-field • Fast trigger chambers: • RPC(barrel) • TGC (end-cap) • Precision chambers: • MDT (barrel and end-cap) • CSC (forward region) • Toroidal magnetic field of 0.5 T: • barrel and two end-cap toroids • complex field ATLAS Marcello Bindi - University and INFN of Bologna - Kruger2010

  7. Muon detection in ATLAS • Trigger: RPC + TGC • Bunch crossing period: 25 ns @ LHC • Trigger chamber time resolution < 10 ns • pT is estimated by on-detector • electronics, according to ΔR w.r.t • infinite momentum line. • pT thresholds cab be adjusted: • from 6 to ~ 40 GeV • Precise PT measurement (MDT+CSC) • Measure magnetic deflection by • toroidal field • 3 planes of precision chambers: • • Barrel: 3 point sagitta measurement • • Endcap: point-angle measurement • pT = 1 TeV ; 500 μm sagitta • 50 μm point resolution needed Marcello Bindi - University and INFN of Bologna - Kruger2010

  8. MonitoredDriftTubed 99.7% of channels working during pp data taking (out of 341K tubes) 0.2% lost forever (i.e. broken wire or not accessible anymore) 0.1% to be fixed in X-mas 2011 or later shutdowns Detector coverage : 100% Space time relationship of the ATLAS MDT chambers. Drift time spectrum in the ATLAS MDT chambers. Marcello Bindi - University and INFN of Bologna - Kruger2010

  9. Resistive PlateChambers • Status of non active Gas Gaps unchanged since several months: • 1% (out of 3592) disconnected from HV due to broken gas inlets; not accessible anymore • 0.6 % disconnected from HV due to excessive gap currents; recoverable during winter shutdown • HV connectors: • About 1 failure/10 days (quickly replaced) ; • anyway no holes thanks to trigger redundancy •  replacement of all connectors already planned Trigger coverage : 99.7 % 1 trigger tower (out of 404) The plots show the Eta and Phi view coincidence of Low/High Pt RPC trigger hits. Marcello Bindi - University and INFN of Bologna - Kruger2010

  10. Thin Gap Chambers • Detector : 98.4% fully operational • 50KHz max Level1 (L1) trigger rate (100KHz after Dec.) • HV Trips when Luminosity steps up (most recovered within 24h) • Maintenance foreseen during next winter shutdown. Trigger coverage : 100.0 % TGC, timing optimization Marcello Bindi - University and INFN of Bologna - Kruger2010

  11. CSC • Detector operational the entire year at 98.5% • Maximum output rate sustainable ~ 70 kHz • 1% data loss due to errors (it will be fixed in December) Marcello Bindi - University and INFN of Bologna - Kruger2010

  12. Detector operation and stability • Stable running conditions during 2010: • Muon detectors “running efficiency” • almost 100% during STABLE beam • periods with DAQ running . • Very good working fractions. • Operational developments: • 4 sub-detectors have unified their procedures, user interfaces and shifters • since the begin of September the HV operations related to LHC beam conditions (injection …) are automatic. • From February one single shifter will supervise the 4 sub-detectors. Marcello Bindi - University and INFN of Bologna - Kruger2010

  13. Trigger performance Marcello Bindi - University and INFN of Bologna - Kruger2010

  14. Muon trigger status RPC • 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 • EF: Full muon reconstruction available • L1, L2 and EF commissioned and used for active rejection. TGC Marcello Bindi - University and INFN of Bologna - Kruger2010

  15. Muon Trigger Efficiencies L1 efficiency, T&P with J/Psi Barrel + 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% EF efficiency, inclusive muon Barrel + End-caps L1 efficiency, inclusive muon Barrel Marcello Bindi - University and INFN of Bologna - Kruger2010 pT> 4 GeV

  16. Muon Trigger vs Luminosity • Measured L1 trigger rates as a function of the instantaneous luminosity for different L1 thresholds. • Extrapolation to higher luminosity based on rates measured with data  fundamental for the trigger strategy. • The steps are due to different filling schemes changing the contribution of cosmic radiation to the trigger rate. Allocated rate Marcello Bindi - University and INFN of Bologna - Kruger2010

  17. Reconstruction performance Marcello Bindi - University and INFN of Bologna - Kruger2010

  18. Muonreconstruction Objective: Muon identification in a wide momentum range from GeV to TeV. 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 Marcello Bindi - University and INFN of Bologna - Kruger2010

  19. Di-muon mass Di-muon invariant mass spectrum for 2010 full data, from fully combined opposite sign muons. Event Filter applies a pT cut at ~15 GeV, which for consistency is reconfirmed offline for one of the two inner detector-muon spectrometer combined tracks (the other one is required to pass a pT threshold of 2.5 GeV). Marcello Bindi - University and INFN of Bologna - Kruger2010

  20. Reconstruction Efficiency from 2009 cosmics data • 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. Turn on curve:Good agreement between Dataand MC ATLAS Preliminary 2009 Cosmic Data ATLAS Preliminary 2009 Cosmic Data Average efficiency: 97.4 ±0.1 % 95.2 ±0.1 % Marcello Bindi - University and INFN of Bologna - Kruger2010

  21. Reconstruction Efficiency from 2010 beam data • Use independent algorithms to assess reconstruction efficiency. • Tag and Probe studies are under preparation with J/Psi and Z. • First results from Z will be available soon. Marcello Bindi - University and INFN of Bologna - Kruger2010

  22. (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- Marcello Bindi - University and INFN of Bologna - Kruger2010

  23. (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 Marcello Bindi - University and INFN of Bologna - Kruger2010

  24. Momentumresolution Marcello Bindi - University and INFN of Bologna - Kruger2010

  25. Momentumresolutionpreformancefrom 2009 Cosmics Muons from Barrel Region Marcello Bindi - University and INFN of Bologna - Kruger2010

  26. Work in progress on resolutionpreformancefrom 2010 Data • Calibration • Precise r-t relations • Precise t0 values • B field corrections to r-t relations •  Objective to reach a MDT hit resolution < 100 μm • Alignment • Improved alignment in few chamber (End-cap) • Use of Toroid off data • Cross checks using high PT tracks • Magnetic Field • - Use of Asymmetric B field map • Results analyses from J/ψ, W and Z Marcello Bindi - University and INFN of Bologna - Kruger2010

  27. Alignment and Calibration status Goal of the alignment: < 50μm ; dominant contribution to the pT resolution for pT>300 GeV barrel alignment±50 mm (large sectors) ±100 mm (small sectors) end-cap alignment±45 mm • Optical alignment system • Barrel: relative • End-caps: absolute • Data with toroidal B-field off. Momentum from inner detector • Measure alignment with straight tracks. 27 Marcello Bindi - University and INFN of Bologna - Kruger2010

  28. Momentum Z resolution performance Zµµ in the Barrel region • Using the Muon Spectrometer and Inner detector • Fit using the following function: Z Breit-Wigner with γ-interference convoluted with one single gaussian resolution function with σZ Marcello Bindi - University and INFN of Bologna - Kruger2010

  29. Z resolution with combined MUON-ID • Oppositely charged Muon pairs with pT>20 GeV • Track isolation cut: Σ(pTtracks) in a cone (η,Ф) of radius < 0.4 is < 0.2 pTµ • |η1, η2|<1.05. • EF triggers used: 10 GeV threshold and 13 GeV for higher luminosity. • Monte Carlo prediction using Pythia-generated Z->µµ events. Marcello Bindi - University and INFN of Bologna - Kruger2010

  30. Improvements after November reprocessing on first 6 pb-1 Marcello Bindi - University and INFN of Bologna - Kruger2010

  31. Conclusions and outlook • Muon detectors have been very stable and fully operational during the whole 2010 data taking. • Performance of detector, trigger and reconstruction have been studied with first data and cosmic events. • Overall performance very close to detector design! • Good agreement between data and MC. Some improvements will be following soon, specially in resolution studies. • Many more results soon to come with the full amount of available data set. • Big expectationsfrom 2011 data takingwithhigherluminosity! Marcello Bindi - University and INFN of Bologna - Kruger2010

  32. Back-up Marcello Bindi - University and INFN of Bologna - Kruger2010

  33. Rpc trigger coverage Eta vs Phi (Strip) Marcello Bindi - University and INFN of Bologna - Kruger2010

  34. L1 trigger efficiency • Trigger efficiency of L1 muon for the lowest threshold MU0 as a function of the offline muon pT obtained with a tag and probe method on Jpsi candidates using combined muons for both the tag and probe tracks. Events are required to have passed the L1 MinBias trigger and a muonEventFilter confirmation. A reconstructed primary vertex with at least 3 Inner Detector (ID) track is required in each event. Muon combined tracks in the eta range [-2.4,2.4] are required to match with a reconstructed primary vertex with z < 10 mm. Only muons associated with ID tracks that have at least one hit in the pixels and six in the SCT are accepted. • The Jpsi candidates have been selected asking for two opposite sign muons and with angular distance 0.4<DR<2.0 and with an invariant mass window between 2860 MeV and 3340 MeV. The tag and probe method has been applied matching the combined muons to muon trigger RoIs using the geometrical criteria DR<0.4. L1 triggers found within +- 3 BCs are included in the efficiency calculation as the RPC L1 timing is not yet fully commissioned. The used data sample corresponds to an integrated luminosity of about 210 nb-1. Marcello Bindi - University and INFN of Bologna - Kruger2010

  35. L2 relative efficiency Efficiency of the L2 muon trigger combining muon spectrometer and inner detector information wrt to the L1 muon trigger as a function of the transverse momentum pT from offline reconstructed combined muons. A cut at L2 is applied to retain muons with pt>4GeV. Marcello Bindi - University and INFN of Bologna - Kruger2010

  36. Timing for RPC and TGC • Big improvement with first few pb-1 in RPC timing • RPC is now close to have 100% events in right BC on both, Low and High pT trigger. • TGC almost there since the beginning of 2010 data taking. Marcello Bindi - University and INFN of Bologna - Kruger2010

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