Precision Drift Chambers for the ATLAS Muon Spectrometer

1
Precision Drift Chambers for the ATLAS Muon
Spectrometer
Abstracts 344,350,646

• 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 Higgs and new physics

• Muon Spectrometer
• toroidal magnetic field ltBgt 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 ? lt 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 !
at 1TeV ? 10 ? sagitta 500 µm
elaborate optical alignment system to monitor
chamber deformations and displacements
chamber resolution 50 µm ? monitoring of high
mechanical precision during production
in this talk
4
Monitored Drift Tube Chambers (MDT)

• 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 ArCO2 (937) 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
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 of only 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 so far
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 in all chambers
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 nominal positions in the
monitoring (MPI)
required accuracy achieved
ltrmsygt 18 µm
10
Cosmic Ray 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
Cosmic Ray 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 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)

, ArCO2(937), 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