MWPC vs. Strawsfor the CMB TRD

C. Garabatos

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

2

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

3

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

4

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

5

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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

8

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

10

Pion rejection: Straws

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

11

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

12

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

14

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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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Effect of inclined tracks: Straws

Position-dependent efficiency

26 mm 4 mm track at 11.5 o

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

17

Leak rate cost

• MWPC

10% vol/year

(1 mbar l/h)

1.5 k€/yr

• Straws

0.2 m3/day

50 k€/yr

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

20

TR performance vs. [Xe]

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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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

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

22

On CF4...

C. Garabatos CBM Collaboration Meeting, GSI 10.03.05

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On ageing...