1. Precision Drift Chambers for the ATLAS Muon Spectrometer
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
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: <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

3. Performance goal: high stand-alone µ-momentum resolution of 2-10% !
at 1TeV:  = 10%
 sagitta = 500 µm
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

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: 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. Drift Tube Production MDT chambers consist of up to 432 drift tubes:
tube wall: 0.4 mm Al
30 mm diameter
wire: 50 µm W-Re
endplug
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 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
<rmsy> = 18 µm

10. Cosmic Ray Test goals: check functionality of all
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
10 µm
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)
, 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 even at highest expected irradiation
extraction of tracking efficiency using the reference track in the Si telescope
track-reconstruction efficiency
for 4m long tubes
total track-reconstruction efficiency:
( )% without irradiation
( )% 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

15. old slides/additional info

16. centering of the wire within a drift tube:
Drift Tube Quality
dark current (0.11 %)
wire tension (0.26%)
gas leak (1.29%)
wire position
apply quality cuts on gas thightness, dark current, ...
 total rejection of 2.6%
centering of the wire within a drift tube:
rms of 7µm
rms x/y = 7 µm
NIKHEF

17. Performance under LHC Conditions
n and  background counting rates in s-1 cm-2
operation at unprecedented
high background rates:
8 – 100 s-1cm-2
performance test of a large 6-layer chamber at CERN:
high energy µ beam (100 GeV)
-ray irradiation (Cs-137 source with 740 GBq)
external reference (silicon beam telescope)

18. Single Tube Resolution
resolution vs. drift radius
, Ar:CO2(93:7), 3 bar
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

19. Performance under LHC Conditions
n and  background counting rates in s-1 cm-2
operation at unprecedented
high background rates:
8 – 100 s-1cm-2
performance test of a large 6-layer chamber at -ray irradiation facility at CERN
(Cs-137 source with 740 GBq)
(external reference)

20. Single Tube Resolution
good resolution even at high irradiation
resolution vs. drift radius
irradiation
<resolution>
no irradiation
104 µm
64 Hz/cm2
111 µm
121 Hz/cm2
116 µm
183 Hz/cm2
125 µm
degradation due to
space charge effect
 for the muon chambers:

21. Efficiencies single tube efficiency high efficiencies also
irradiation
rate / tube
 [%]
none
99.70 ± 0.02
64 Hz/cm2
73 kHz
99.62 ± 0.02
121 Hz/cm2
138 kHz
99.60 ± 0.02
183 Hz/cm2
209 kHz
99.55 ± 0.03
high efficiencies also
at high rates
3 probability of real hit
track-reconstruction efficiency
for different numbers of track hits
irradiation
3 [%]
no irradiation
93.3 ± 0.2
64 Hz/cm2
89.8 ± 0.2
121 Hz/cm2
86.1 ± 0.2
183 Hz/cm2
80.3 ± 0.3
even at high level of irradiation
efficient tracking possible
3 at no irradiation  1 due to  e‘s

22. Status of Chamber Production at Different Sites