Status & Readiness of the ATLAS Muon Spectrometer

1. Status & Readiness of the ATLAS Muon Spectrometer Workshop of the Americas NYU August 4, 2009 J. Chapman - University of Michigan on behalf of the ATLAS Muon Groups Particular Thanks to C. Ferretti, D. Levin, E. Diehl & A. Belloni (Harvard)

2. Overview Status • Hardware almost completed • Status at closure: • MDT Endcap fibers replaced • RPC nearing 95.5% coverage • TGC ready soon, after 7 months • ATLAS DAQ functioning well • CSC working to reach design L1 rate • Most data from 2008 runs • Muon Sub-detector will be ready for collisions!

3. Outline • Very Quick Detector Description • Sub-detectors Status • Detector Control System Status • Challenges to Precision Calibration • Alignment System – next talk • Commissioning Results • Conclusions

4. ATLAS Muon Spectrometer • Three stations in an air-core toroidal magnetic field (superconducting) (barrel:|η|<1.4 , endcap:1.6<|η|<2.7) • Four different technologies: • Monitored Drift Tubes (MDT): precision chambers in the bending direction • Cathode Strip Chambers (CSC): precision chambers at |η|>2.0 • Resistive Plate Chambers (RPC): trigger |η|<1.05 + 2nd coordinate • Thin Gap Chambers (TGC): trigger 1.05<|η|<2.4 + 2nd coordinate • Performance goal: stand-alone Δp/p~10% at 1 TeV  sagitta ~ 500 μm along Q measured with a resolution ~50μm

5. Spectrometer Layout Side View Muons cross 3 layers of precision chambers for sagitta measurement Trigger chambers are placed on both sides of middle precision layer (+ a few elsewhere) Beam View

6. Monitored Drift Tubes Chambers in DAQ (2009) • System features low failures • Readout channels: ~0.2% • T-sensors: ~0.3% • B-sensors: ~0.5% • Alignment: ~1-2% • Final actions taken • Fiber replacement C & A side • Replaced a few faulty cards & sensors, sealed gas leaks • Switched barrel mezzanines to 50MHz & exchanged a few cards that did not operate successfully at higher speed • Single-hit efficiency above 99% • Hit resolution near design value

7. MDT Occupancy 1090/1150 Chambers installed – 99.6% operational TGC vs MDT correlation Lines ↔ noisy channels MDT Occupancy – chamber Φ vs η Hot spots due to access shafts circled

8. EE Chamber Installation • Additional MDTs • EEL Sector 5 installed • Mounted on Toroid • Other sectors soon • EELA11 next • EELA14 follows • Side C follows A • Schedule is uncertain

9. RPC Status • 95.5% operative (out of 396 towers) • < 4% broken HV connectors or electronic components • < 1% leaky gas channels • Temperature problem forces top sectors to run at 9.2kV (9.6kV)

10. RPC Performance • Cosmic data provides good evaluation of RPC • Hit efficiency in the high 90% region – expect the tails to be reduced with HV tuning • Resolution is as expected • Timing calibration for trigger is underway

11. RPC Performance with MDT tracks - Events triggered by RPCs with ¾ majority - Only 1 MDT track reconstructed by MuonBoy - Look at 4th layer when trigger justified offline by 3 layers From: G.Aielli BM BM 113860 113860 Efficiency for BM chambers with HV=9.6kV, Vth=-1V Residual distribution normalized to strip pitch

12. TGC Status • All chambers installed with final gas CO2:n-C5H12(55:45) • Now: 3 chambers (less than 0.8‰) are problematic • TGC trigger worked very well during DAQ periods Fall 2008 data TGC trigger timing

13. TGC Performance • Low rate of faulty channels • ~0.02% in Middle Layer • ~0.5% in Inner Layer • No holes in coverage • L1 rate limited to 45kHz • Redundant information removed. Ready for tests • Last runs (HV+gas) in 2008 • MDT/TGC work halted runs • Oil contamination of gas damaged vessel. System will be back mid August 2009

14. CSC Status • 2 of 128 panels unusable • covered by redundancy • New ROD firmware progress • Current status: max L1 rate < 1kHz; • ROD crashes after ~1k events fixed • Test stand & two SLAC engineers at CERN for redesign effort • Commissioning the CSC with cosmics is difficult • Low probability to hit CSC • Only 50k events in 2008 with 199, 4-hit segments in CSC.

15. Securing & Maintaining Precision • Knowing the drift time R-T function & offset t0. • Depends on gas temperature, composition, & pressure • Depends on pulse amplitude (time walk) & wire sag • Depends on electronics delays & trigger timing (t0) • Knowing the chamber alignment & B-field • Sensitivity figures: • Drift velocity at wall is ~20μm/ns (50μm in 2.5ns) • Dt of 7oC corresponds to ~ 17ns ( many s) • Wire sag for largest chambers ~ 500mm • Plots for other variables visible in gas monitor

16. MDT Detector Control System • The DCS provides initialization of the chambers and reads out • voltages/temperatures of ~18k F.E. electronic cards and power supply • over 13k temperature sensors • ~2k Hall probes • gas parameters • alignment system • ... • Note: 7oC variation from bottom to top! T>25°C T<18°C

17. MDT Gas Monitoring & PromptCalibrations Recycler (D. Levin, N. Amram et al) gas supply line • Track gas quality via maximum drift time • Compare behavior of MDT gas for supply and exhaust lines • Precision: below 1ns in the maximum drift time measurement, once/hour • Universal Time-to-Radius (RT) relations published every two hours • Gas volume exchange • Muon Spectrometer • ~2 weeks refresh • Gas Monitor • ~2 hours gas exhaust 16 4-August-2009

18. MDT gas Drift-time (Tmax ) & Cavern Humidity ns Dt = 720-685ns = 35ns Oct 2007 Dec 2008 • Monitoring TDC spectra continuously since August 2007 • Results displayed at mdtgasmon.grid.umich.edu • Transients due to gas system interventions or occasional component failures • Overallvariation in maximum drift time caused by gas mixture change from • External humidity • Intentional water vapor injection

19. MDT Calibration with Cosmic-rays • Difficult due to asynchronous nature of cosmic rays with LHC clock  25ns and variable TOF between trigger and precision chambers. Recovered by t0-tuning algorithm. • Dedicated L2 stream  3 centers for all chambers in 24h • Collision data critical to obtain final precision Residuals vs. Radius t0fit

20. Segment Reconstruction Performance • Performance from clean sample: • No shower (#segments/event<20) • Track passing at least 2 stations • Extrapolation pass the 3rd station • Segment on each station Outer layers Inner layer Efficiency(ε)= #Seg(found)/#Seg(expect) • For cosmic rays • enlarged single-hit error (1 mm) • relaxed matching angle • minimum 3 hits per segment Fall 2008 <ε>=98.4%

21. Track Reconstruction MDT hits distribution peaked at 12, 14 and 20 (expected) Tails: overlap small-large sectors Number of hits • Track residual ~ 250 μm worse • than segment residual (expected): • misalignment • multiple scattering

22. Inner Detector vs. Spectrometer ΔP[GeV/c] Cosmic ray passing in the Inner Detector split in two tracks at the perigee. 3 GeV loss in the calorimeter. MS tracks corrected for the Eloss compared with ID tracks Δp(top-bottom) 2 x 3 Gev loss in calorimeters

23. Conclusions • Hardware: status very good (nearing completion) • Trigger: • Coverage much improved from 2008 • Timing between detector elements still being tuned • Calibration: • Calibration centers returning constants in 36 hours • Fine tuning of constants awaiting collision data • Alignment: Chamber position & orientation known • Track segment finding, reconstruction efficiency, & resolution is improving & will continue to improve Still a lot of work to do, but the ATLAS Muon Spectrometer is ready for beam

24. Backup Slides Alignment Issues

25. Layers, Locations, & Labels EM EO EI

26. Fake Segments Form pattern recognition: 1 track should to give 1 segment/station From noise hits: study #segments far from the only track in the event Fall 2008 avg=2.3·10-4 Fall 2008 avg=1.1

27. ATLAS Muon Detector Endcap 1.05<|η|<2.7 three wheels (Small, Big, Outer) of TGC + MDT/CSC Barrel |η|<1.05: I=inner, M=middle, O=outer layers of RPC + MDT in S=small and L=large sectors

28. MDT/CSC Status • 1090/1150 MDT + 32/32 CSC chambers installed • Shutdown: recovered ~7k MDT tubes, replaced MDT BW optical fibers, doubled speed for all MDT readout electronics • Now: > 99.5 % MDT channels operational and 99.9% of the chambers are read by the ATLAS DAQ + 98.5 % CSC layers • Work continuing on CSC readout Driver (ROD) firmware Inner, Middle and Outer MDT occupancy (Fall 08): sector vs. ηID

29. Precision Chambers Alignment • Grid of ~12k optical sensors monitoring/reconstructing chamber position, rotation angles and deformations • Track-based alignment used for global positions (Endcap Wheels-Barrel and Spectrometer-ID) • After shutdown over 99% of the devices working and the degradation due to a few missing sensors is negligible Barrel Endcap

30. Barrel Alignment: Large vs. Small Sectors

31. Alignment in the Barrel • 105μ±(20 GeV) enough to align at 30 μm (Small sectors: 5×statistics) • Initial geometry + alignment traces displacement in relative mode • Track + alignment parameters inside one global fit (correlations included) • Tracks (magnetic field off runs) • Close to the IP (precision plane) • Traversing 3 stations • Straight line fit inner-outer MDT • Residuals in the middle chamber ~ sagitta = 22±7 μm

32. Alignment in the Endcap • Corrected sagitta = 2±27 μm • 3 segments tracks (EI-EM-EO) in the same sector • Angle segments-straight line EI-EO segments < 5/50 mrad (sagitta only) • At least 1 trigger phi hit (good 2nd coordinate measurement)

33. Spectrometer Overview • Designed to trigger on and measure muons with Pt ≳ 3 GeV with resolution 3% < 250 GeV to 10% @ 1 TeV. • Magnetic field from air-core torroids: barrel + 2 endcap • Trigger detectors (trigger + 2nd coordinate measurement) • 0<η<1.0 (Barrel) Resistive Plate Chambers (RPC) 373k chan • 1.0<η<2.4 (Endcap) Thin Gap Chambers (TGC) 318k chan • Precision detectors • 0<η<2.0 Monitored Drift Chambers (MDT) 354k chan • Monitored ⇨Positions monitored by an alignment system • 2.0<η<2.7 Cathode Strip Chambers (CSC) 30.7k chan • Alignment – determine chamber positions to ~50 μm • Separate optical alignment systems for barrel & endcap complemented by alignment with tracks.