MWPC vs. Straws for the CMB TRD
description
Transcript of MWPC vs. Straws for the CMB TRD
MWPC vs. Strawsfor the CMB TRD
C. Garabatos
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Gas mixture
• MWPC: Xe-CO2 [85-15] or other concentrations
• Straws:– ATLAS
• originally Xe-CO2-CF4 [70-20-10]
• now Xe-CO2-O2 [70-27-3]
– Proposed for CBM: Xe-CO2 [75-25]
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Active volume
RADIATOR
RADIATOR
gas
gas
Straw tubes: 79%
...or twice the material
GAS
RADIATOR
MWPC: 100%
...but need reinforcement
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Occupancy, granularity
• MWPC: Pad size chosen to match occupancy and resolution in the bend direction.
• Straws: Straw length chosen to match occupancy.
TSR layers channels occupancy
MWPC 9 550 000 10 %
Straws 18 300 000 18 %
At the end, the number of channels should be equal for equal occupancy
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Resolution, rate capability
0.0 0.2 0.4 0.6 0.8-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Indu
ced
sign
al (
a.u.
)
Time (s)
4 mm straw, 20 m wire 4 mm straw, 30 m wire 6 mm thick, 4 mm pitch 4 mm thick, 2 mm pitch
Garfield simulations, no electronics
Xe-CO2 [85-15]
Average induced signal on anodesat gain=104,normalised
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Resolution, rate capability
• MWPC
First estimation from test beam data
0 20 40 60 80 100 120200
220
240
260
280
300
(
m)
Rate (kHz/cm2)
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Resolution, rate capability
• Straws:
CBM rates no problem for the straw tubes
Resolution worse than quoted
500 kHz/cm2
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Efficiency MWPC
Preliminary measurements
≈ 90 % at 100 kHz/cm2
0 20 40 60 80 100 12050
60
70
80
90
100
Eff
icie
ncy
(%
)
Rate (kHz/cm2)
GSI1 (2 mm) GSI2 (4 mm)
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Efficiency Straws
≈ 70-80 %at 100 kHz/cm2
500 kHz/cm2
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Pion rejection: Straws
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Pion rejection: MWPC
• Radiator and number of layers to be optimised in both cases: compromise with material
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Segmentation MWPCI II III
• Increasing segmentation, determined by chamber size• Small cracks (frames, services)
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Segmentation Straws
• Many dead areas• Cracks with material (end-plugs, electronics, services)• Non-projective geometry Need a careful estimation of coverage and radiation length
I II III
C. Garabatos CBM Collaboration Meeting, GSI 10.03.05
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Material budget
• MWPC
Radiator: 0.2-0.5
Chamber: 0.25
Electronics: 0.9
Total: 1.35-1.65 %
[X/X0]
(with reinforcement)
• Straws
?
probably higher
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Effect of inclined tracks: MWPCTracks at 30o release ionisation in a finite region along the pads
Degradation of resolution with angleTrack matching easier at large anglesAngle can be minimised by leaning detectors
0 1 2 3 40
50
100
150
200
250
300
En
trie
s
Average electron position (mm)
= 401 m
eTR
= 440 m
TR
Garfield simulation, 30o incident angle
-5 0 5 10 15 20 25 30 350
100
200
300
400
500
600
Res
olu
tio
n (m
)
Angle (degrees)
1 GeV 1 GeV e- + TR Measured
6mm MWPC 2 mm pitch, 7.5 mm pads
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Effect of inclined tracks: Straws
Position-dependent efficiency
26 mm 4 mm track at 11.5 o
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Leak rate cost
• MWPC
10% vol/year
(1 mbar l/h)
1.5 k€/yr
• Straws
0.2 m3/day
50 k€/yr
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One little detail: stabilityATLAS straw tubes use >30 m anode wires andO2 (formerly CF4) gas in the mixture
Xe-CO2-CF4
Streamers
NIM A 337 (1993) 122-126
55Fe
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Consequences
• Because of large anode diameter:– Electron attachment agents are needed– Large amount of quencher is needed
– Can straws be operated with Xe-CO2?
R&D needed to optimise straw geometry and gas mixture
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TR performance vs. [Xe]
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Conclusions
• Comparable performance (to 1st order)
• Multiple scattering will probably drive the tracking performance: need good estimates of material budget
• Stability and gas for the straws to be clarified
• Both detectors would need substantial R&D to be ready for CBM
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On CF4...
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On ageing...