Precision Drift Chambers for the ATLAS Muon Spectrometer

1. Abstracts: 344,350,646 Precision Drift Chambers for the ATLAS Muon Spectrometer Susanne Mohrdieck Max-Planck-Institut f. Physik, Munich for the ATLAS Muon Collaboration International Europhysics Conference on High-Energy Physics 17.-23.7.2003 Outline: • Introduction - ATLAS and the muon spectrometer • Precision chamber production • Monitoring and measurement of chamber quality/accuracy • Performance test of precision chambers under LHC operating conditions

2. The ATLAS Muon Spectrometer ATLAS at LHC: multi-purpose detector to search for Higgsand new physics • Muon Spectrometer: • toroidal magnetic field: <B> = 0.4 T •  high pt-resolution independent • of the polar angle • size defined by large lever arm to • allow high stand-alone precision • air-core coils tominimise the • multiple scattering • 3 detector stations • - cylindrical in barrel • -wheels in end caps • coverage: || < 2.7 • used technologies: • fast trigger chambers: • TGC,RPC • high resolution tracking • detectors: MDT, CSC

3. see talk by C.Amelung Performance goal: high stand-alone µ-momentum resolution of 2-10% ! at 1TeV: = 10%  sagitta = 500 µm elaborate optical alignment system to monitor chamber deformations and displacements chamber resolution: 50 µm  monitoring of high mechanical precisionduring production in this talk

4. Monitored Drift Tube Chambers (MDT) • 6 / 8 drift tube layers,arranged in • 2 multilayersglued to a spacer frame • length: 1 – 6 m, width: 1 – 2 m • optical system to monitor chamber • deformations • gas: Ar:CO2 (93:7) to prevent aging, 3 bar • chamber resolution: 50 µm • single tube resolution: 100 µm • required wire position accuracy: 20 µm Barrel End Cap

5. Status of MDT Production • production at 13 sites in 7 countries: • assembly layer by layer using • precision table with precise ‚combs‘ • on-line monitoring of temperature • and mechanical movements MPI Munich Plan for Bare Chambers Bare Chambers Chambers with Services • production within schedule: • 58% of 1194 chambers assembled • will be finished middle of 2005

6. tube wall: 0.4 mm Al 30 mm diameter endplug wire: 50 µm W-Re Drift Tube Production MDT chambers consist of up to 432 drift tubes: • precise wire positioning • in the endplugs: • rms of 7µm production at NIKHEF • automated wiring machine • elaborate quality checks • total rejection ofonly 2.6% • 73% of in total 370.000 tubes • produced

7. Wire Positions with a X-Ray Method measurement of the intensity as function of the motor position X-tomograph at CERN accuracy of wire position measurement: 3 µm mechanical precision measured with X-ray method selected chambers tested: 74 of 650 chambers produced at 13 sites scanned sofar average wire positioning accuracy: 15 µm

8. Monitoring of Chamber Quality monitoring of the chamber parameters by optical sensors during the production (e.g. MPI f. Physik, Munich) X-rayed MPI chambers 20 µm • stable over time • agreement with X-ray method 40 µm

9. Monitoring of Wire Positions • combination of all monitoring results: • - chamber parameters • - tube positions within a tube layer • wire positions within the tube wire positions inallchambers deviations of monitoring to X-ray method • good agreement between X-ray • method and monitoring results • y = ymonitoring – yX-ray • - average rms(y) = 19 µm MPI • comparison to nominal positions: • - stable wire positioning accuracy • - average rmsy = 18 µm rms of deviations from nominalpositions in the monitoring (MPI) required accuracy achieved <rmsy> = 18 µm

10. CosmicRay Test e.g. Test Facility at the University of Munich • goals: • check functionality of all • tubes and electronics channels • measurement of wire positions y z • deviations from nominal positions compared • to X-ray results: rmsy = 25 µm, rmsz = 9 µm

11. 10 µm CosmicRay Test (cont) • good agreement with X-ray • results • extraction of layer positions • with high precision: 2 µm in z • 4 µm in y z displacement for the tube layers 0.4 µm • precision for z-pitch: • 0.3 µm per layer z-pitch for the tube layers University of Munich

12. Performance under LHC Conditions • operation atunprecedentedly • high n and  background rates: • 8 – 100 s-1cm-2 • performance test of a large 6-layer chamber: • high energy µ beam (100 GeV) • -ray irradiation (Cs-137 source with 740 GBq) • external reference (silicon beam telescope) , Ar:CO2(93:7), 3 bar Single Tube Resolution • required resolution maintained even • at high irradiation: • 104 µm without irradiation • degradation by 10 µm at highest • ATLAS rates of 100 s-1cm-2 degradation due to space charge fluctuations single tube resolution vs. drift radius

13. Efficiencies extraction of tracking efficiency using the reference track in the Si telescope track-reconstruction efficiency for 4m long tubes • total track-reconstruction efficiency: • ( 99.97 )% without irradiation • ( 99.77 )% at highest ATLAS rate • (for 4m long tubes) +0.03 - 0.9 +0.23 - 0.8 highest ATLAS rate • even at highest expected irradiation no deterioration of track-reconstruction efficiency

14. Conclusions • Precision MDT chamber production within schedule (58% assembled) • Wire positioning measured with several methods during production •  required accuracy of 20 µm achieved • Performance under LHC conditions tested •  at highest background rates chamber resolution of 50 µm maintained •  no deterioration of track-reconstruction efficiency