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Proposal for MAPMTs as Photodetectors for the LHCb RICH

This proposal outlines the use of Multianode Photo Multiplier Tubes (MAPMTs) as photodetectors for the LHCb RICH system. The proposal covers the introduction, R&D results, baseline design, and conclusion by Franz Muheim. MAPMTs offer single-photon sensitivity, good spatial resolution, and a large active area fraction, meeting the stringent requirements for the LHCb experiment. The proposal details the MAPMT specifications, results of bench tests and beam setups, photon yields with and without quartz lenses, analyses of charged particles impact, and magnetic field tests. The baseline design includes tilted modules with 4x4 arrays, bleeder boards, and mu-metal shields. Overall, the proposal demonstrates that commercial MAPMTs fulfill the LHCb RICH specifications effectively.

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Proposal for MAPMTs as Photodetectors for the LHCb RICH

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  1. Proposal for MAPMTs as Photodetectors for the LHCb RICH Franz Muheim University of Edinburgh on behalf of the MAPMT group F.Muheim

  2. Outline • Introduction • Multianode Photo Multiplier Tubes • R&D Results • Baseline Design • Conclusion F.Muheim

  3. Photo Detector Requirements Photo detector area: 2.9 m2 • Single photon sensitivity (200 - 600 nm) with quantum efficiency > 20% • Good granularity: ~ 2.5 x 2.5 mm2 • Large active area fraction:  73% • LHC speed read-out: 40 MHz Options: MAPMT or HPD F.Muheim

  4. MAPMT Multianode Photo Multiplier Tube • Combines single photon sensitivity with good spatial resolution • 8x8 dynode chains Gain: 3.105 at 800 V • Manufacturer: Hamamatsu • 1 mm flange removed, packing fraction increases by 14 % F.Muheim

  5. MAPMT R7600-03-M64 Quantum efficiency • Bialkali photo cathode, QE = 22% at  = 400 nm • UV glass window replaces borosilicate, QE dE increased by 50 % F.Muheim

  6. Quartz Lenses • MAPMT active area fraction: 38% (includes pixel gap) • Increase with quartz lens with one flat and one curved surface to 85% F.Muheim

  7. Bench Tests Pixel scan with LED Single channel spectrum (LED) • Collection efficiency not very uniform (~20%) • Gap between pixels: 0.2 mm • 40 MHz read-out electronics • Average signal/ pedestal width = 40:1 • Signal loss: 11.5 % (includes 2.5% for no multiplication at 1st dynode) F.Muheim

  8. Test Beam Set-up F.Muheim

  9. Single MAPMT Test Beam • CAMAC electronics • RICH 1 prototype Photo electron yield Good agreement F.Muheim

  10. Single MAPMT Test Beam Cherenkov angle resolution • CAMAC electronics • RICH 2 prototype • Focal length: 4 m • Angular resolution • 0.27 mrad (data) • 0.26 mrad (MC) Good agreement F.Muheim

  11. LHC Speed Electronics F.Muheim

  12. LHC Speed F/E Electronics F.Muheim

  13. Test Beam Set-up • Cluster with quartz lenses • Bleeder board • Cluster: 40 MHz Read-out F.Muheim

  14. Cluster Test • 9 MAPMTs read out with 6 boards • 5  threshold cut, common-mode subtracted • Lots of photons, but cross-talk CF4 Radiator, 700 mbar HV = -1000 V F.Muheim

  15. Cross-Talk Probability that pixel y causes hit in pixel x • Asymmetric cross-talk (board 9) • Correlated to neighboring APV Sample channels • Not correlated with neighboring pixels in tube F.Muheim

  16. Cross-Talk Probability that pixel y causes hit in pixel x • Symmetric cross-talk • Correlated with APV input neighbors (ceramic) • Cross-talk source is electronics • MAPMT do not have large cross-talk F.Muheim

  17. Photon Yields With quartz lenses • Cross-talk correction applied • Observe 6.4 photo electrons per event • Background: 0.41 p.e. • Few dead pixels • Yield of different tubes F.Muheim

  18. Photon Yields No lenses Quartz lenses • Ratio with/without lenses = 1.45, expected 1.50 F.Muheim

  19. Photon Yields • Analysis includes • Common-mode subtraction • Cross-talk correction • Background subtraction • Signal loss & dead pixel correction • Results: Preliminary Good agreement F.Muheim

  20. Photon Yields Single events Number of photo electrons F.Muheim

  21. Charged Particles • Charged particles traversing the lens & MAPMT produce background hits • Angle scan F.Muheim

  22. Multiplicities • Multiplicity from charged particles •  [5..10] for for most angles • up to 30 for angles around 45o For MAPMTs, charged particles are a small background F.Muheim

  23. Magnetic Field Tests • LED • Pin hole mask • -metal shield • MAPMT tested with • Helmholtz coil • 0, 10, 20, 30 Gauss F.Muheim

  24. No Shielding • MAPMTs are insensitive to transverse magnetic fields up to 30 G • Expect mainly By field • By = 21 ..27 G (RICH 1) • By = 150 G (RICH 2) reduce by ~ 15 with shielding of planes • Sensitive to longitudinal fields  10 G, at 30 G lose 50% top or bottom row (18% average) F.Muheim

  25. With -Metal Shielding • -metal: t = 0.9 mm • Extension: d = 10, 13, 32 mm • Reduced loss at 30 G • 7 .. 25 % worst row (d=10,13 mm) • no structure (d = 32 mm) • Expect low Bz field • Bz = 0 .. 5 G (RICH 1) • Bz = 0 .. 38 G (RICH 2) reduce by ~ 15 with shielding of planes F.Muheim

  26. MAPMT R & D Summary • Successfully tested close-packed 3x3 array of MAPMTs • Quartz lenses work as expected • Measured photon yield in agreement with simulation • Demonstrated 40 MHz read-out Commercial MAPMT fulfils LHCb RICH specifications F.Muheim

  27. Baseline Design Tilted Modules • Pointing geometry • 4x4 array, 1024 channels • Bleeder board with 8 F/E chips • -metal shield • Pixel size at lens: 3.0 x 3.0 mm2 • Filling factor: 0.79 F.Muheim

  28. Half Planes RICH 1 RICH 2 • Total 232 modules, 3504 tubes • Outermost modules only partially equipped •  = 440 mrad • 5 columns • 10 rows •  = 240 mrad • 6 columns • 11 rows F.Muheim

  29. Integration MAPMT geometry RICH 1 integration • MAPMT pitch: 26.7 mm • Module pitch: 108.8 mm • -metal shield: 0.4 mm • Mounting frame: carbon fibre, G10 • Little distance between Vertex tank and RICH 1 Tracker 1 must also fit • Cooling for 8.8 W /module MAPMT  RICH 1 Vertex tank F.Muheim

  30. F/E Electronics Single photon signal: 300’000 e • Characteristics • Spread: 3 • Signal/pedestal width: 60:1 • Dynamic range: 3 photons 5000 … 1’560’000 e • Attenuation: 6 • F/E chip input: • Noise/ dynamic range: 833 ... 260’000 e • ADC bits: 9 • Occupancy: 3 % F.Muheim

  31. F/E Electronics Baseline • APVm chipnot suitable (shaping time) • SCTA128 is baseline (analogue) • Changes necessary to existing chip • Back-end (32 multiplexing), same as for the vertex detector • Gain adaptation for MAPMT signals, attenuation, additional work • Alternative:BEETLE chip • when it becomes available F.Muheim

  32. L0 & L1 Electronics • Level 0: • # of modules / # of chips: 232 / 1856 • # of channels per module: 1024 • # of channels total: 224256 • # of data links: 7424 • Level 1: • Bandwidth (3% occ.) 85/7.7 Gbits/s with/ without Zero suppression • # of VME modules: 78 • # of multiplexers: 5 F.Muheim

  33. Performance • Performance study  Guy Wilkinson • Preliminary results: • Identification efficiencies • : 86 %, K : 87 % • Fake rates • : 1.4 %, K : 3.0 % F.Muheim

  34. Schedule   • Photo detectors must be ready by 1/7/2004 • Testing takes  2 years • Must place order by 1/3/2001 • Photo detectors are on critical path • F/E electronics design by 1/10/2000 today 1/7/2004 F.Muheim

  35. MAPMT Test Station • Automated test bench • LED or Laser light source • Optical stages • Measure gain of each tube, pixel scan • HV scan • QE measurements (~10% of tubes) • Monochromator • Calibrated standard • Measure Cherenkov light (~10% of tubes) •  source in quartz bar & MWPC F.Muheim

  36. MAPMT Costs Unit cost Cost Subtotal • Tube [kSFr] [kSFr] [kSFr] • MAPMT 0.931 3262 • Lenses 0.070 245 3507 • Level 0 • F/E chip, hybrid 0.200 371 • Motherboard 2.000 464 • TTC, DCS, Data Links 135 970 • Level 1 • 9U VME boards 5.000 390 • Links, crates, MUX, RU, etc 199 589 • Total cost: 5066 F.Muheim

  37. Risk Assessment • Baseline design is very close to what we have already tested • MAPMT photon yield and  resolution • LHC speed read-out electronics • Close packing (quartz lenses) • Commercial photo detector • Possible delays, Note: LHCb is tomorrow • Manpower • Cost F.Muheim

  38. Risk Assessment • Performance • Photon yield, angular resolution • Charged particles • Magnetic stray fields • Electronics • Adapt F/E chip • Not on critical path • Stability • Radiation damage • HV F.Muheim

  39. Risk / Improvements • Further improvements possible • 2-3% higher QE is possible (manufacturer)  9 -14 % more photons • Incorporate lens into vessel window 8% more photons • Optical coupling between lens & MAPMT  8% more photons • Use 4  threshold cut  Smaller signal loss • Binary electronics Cost savings F.Muheim

  40. Conclusions • Results of the MAPMT R&D program • Device performs according to specifications • LHC speed read-out demonstrated • Baseline design presented • Mechanics, Electronics, Integration • Schedule, Cost is a viable choice as photo detector for MAPMT F.Muheim

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