1. Precision Drift Chambers for the ATLAS Muon Spectrometer Susanne Mohrdieck Max-Planck-Institut f. Physik, Munich for the ATLAS Muon Collaboration Abstracts: 344,350,646 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 Higgs and new physics Muon Spectrometer: toroidal magnetic field: = 0.4 T  high p t -resolution independent of the polar angle size defined by large lever arm to allow high stand-alone precision air-core coils to minimise 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. Performance goal: high stand-alone µ-momentum resolution of 2-10% ! chamber resolution: 50 µm  monitoring of high mechanical precision during production elaborate optical alignment system to monitor chamber deformations and displacements see talk by C.Amelung in this talk at 1TeV:  = 10%  sagitta = 500 µm

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

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 production within schedule: 58% of 1194 chambers assembled will be finished middle of 2005 Plan for Bare Chambers Bare Chambers Chambers with Services MPI Munich

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

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

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

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

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

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

12. Performance under LHC Conditions degradation due to space charge fluctuations required resolution maintained even at high irradiation: 104 µm without irradiation degradation by 10 µm at highest ATLAS rates of 100 s -1 cm -2 single tube resolution vs. drift radius, Ar:CO 2 (93:7), 3 bar operation at unprecedentedly high n and  background rates: 8 – 100 s -1 cm -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) Single Tube Resolution

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

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