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