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MWPC vs. Straws for the CMB TRD

MWPC vs. Straws for the CMB TRD. C. Garabatos. Gas mixture. MWPC: Xe-CO 2 [85-15] or other concentrations Straws: ATLAS originally Xe-CO 2 -CF 4 [70-20-10] now Xe-CO 2 -O 2 [70-27-3] Proposed for CBM: Xe-CO 2 [75-25]. Straw tubes: 79%. MWPC: 100%. ...or twice the material.

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MWPC vs. Straws for the CMB TRD

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  1. MWPC vs. Strawsfor the CMB TRD C. Garabatos

  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] CBM Collaboration Meeting, GSI 10.03.05

  3. Straw tubes: 79% MWPC: 100% ...or twice the material ...but need reinforcement Active volume 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. • At the end, the number of channels should be equal for equal occupancy CBM Collaboration Meeting, GSI 10.03.05

  5. Resolution, rate capability Average induced signal on anodes at gain=104, normalised CBM Collaboration Meeting, GSI 10.03.05

  6. Resolution, rate capability • MWPC First estimation from test beam data CBM Collaboration Meeting, GSI 10.03.05

  7. Resolution, rate capability • Straws: CBM rates no problem for the straw tubes Resolution worse than quoted 500 kHz/cm2 CBM Collaboration Meeting, GSI 10.03.05

  8. Efficiency MWPC e ≈ 90 % at 100 kHz/cm2 Preliminary measurements CBM Collaboration Meeting, GSI 10.03.05

  9. Efficiency Straws e ≈ 70-80 % at 100 kHz/cm2 500 kHz/cm2 CBM Collaboration Meeting, GSI 10.03.05

  10. Pion rejection: Straws 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 CBM Collaboration Meeting, GSI 10.03.05

  12. Segmentation MWPC I II III • Increasing segmentation, determined by chamber size • Small cracks (frames, services) CBM Collaboration Meeting, GSI 10.03.05

  13. Segmentation Straws I II III • Many dead areas • Cracks with material (end-plugs, electronics, services) • Non-projective geometry • Need a careful estimation of coverage and radiation length 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 CBM Collaboration Meeting, GSI 10.03.05

  15. Effect of inclined tracks: MWPC Tracks at 30o release ionisation in a finite region along the pads Degradation of resolution with angle Track matching easier at large angles Angle can be minimised by leaning detectors CBM Collaboration Meeting, GSI 10.03.05

  16. Effect of inclined tracks: Straws Position-dependent efficiency CBM Collaboration Meeting, GSI 10.03.05

  17. Leak rate Þ cost • MWPC 10% vol/year (1 mbar l/h) 1.5 k€/yr • Straws 0.2 m3/day 50 k€/yr CBM Collaboration Meeting, GSI 10.03.05

  18. Xe-CO2-CF4 55Fe Streamers NIM A 337 (1993) 122-126 One little detail: stability ATLAS straw tubes use >30 mm anode wires and O2 (formerly CF4) gas in the mixture CBM Collaboration Meeting, GSI 10.03.05

  19. 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 CBM Collaboration Meeting, GSI 10.03.05

  20. TR performance vs. [Xe] CBM Collaboration Meeting, GSI 10.03.05

  21. 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 CBM Collaboration Meeting, GSI 10.03.05

  22. On CF4... CBM Collaboration Meeting, GSI 10.03.05

  23. On ageing... CBM Collaboration Meeting, GSI 10.03.05

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