precision drift chambers for the atlas muon spectrometer susanne mohrdieck max-planck-institut f....
TRANSCRIPT
Precision Drift Chambers for the ATLAS Muon Spectrometer
Susanne MohrdieckMax-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
The ATLAS Muon SpectrometerATLAS at LHC: multi-purpose detector to search for Higgs and 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 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
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
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:CO2 (93:7) to prevent aging, 3 bar
• chamber resolution: 50 µm single tube resolution: 100 µm required wire position accuracy: 20 µm
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
MDT Production (all sites)
0
200
400
600
800
1000
1200
1400
Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 Jan-03 Jul-03 Jan-04 Jul-04 Jan-05 Jul-05 Jan-06
Time
No
. C
ham
bers
Plan Bare Chambers
Bare Chambers
Chambers with Services
production within schedule:
• 58% of 1194 chambers assembled
• will be finished middle of 2005
Plan for Bare ChambersBare ChambersChambers with Services
MPI Munich
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
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 measuredwith X-ray method
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
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 = ymonitoring – yX-ray
- average rms(y) = 19 µm
• comparison to nominal positions: - stable wire positioning accuracy - average rmsy = 18 µm
required accuracy achieved
deviations of monitoring to X-ray method
rms of deviations from nominal positionsin the monitoring (MPI)
MPI
wire positions in all chambers
<rmsy> = 18 µm
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: rmsy = 25 µm, rmsz = 9 µm
z
y
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
Performance under LHC Conditions
degradation due tospace charge fluctuations
required resolution maintained even at high irradiation:
• 104 µm without irradiation • degradation by 10 µm at highest ATLAS rates of 100 s-1cm-2
single tube resolution vs. drift radius
, Ar:CO2(93:7), 3 bar
operation at unprecedentedly 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)
Single Tube Resolution
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
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