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Marco Musy

Aerogel as Cherenkov radiator for RICH detectors. Marco Musy. INFN and Universit y of Milano-Bicocca. Pylos, June 2002. The LHCb experiment. Proton-proton interactions at √ s = 14 TeV at LHC. Particle ID needed between 1-150 GeV/c. Two RICH systems with 3 Cherenkov radiators.

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Marco Musy

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  1. Aerogel as Cherenkov radiator for RICH detectors Marco Musy INFN and University of Milano-Bicocca Pylos, June 2002

  2. The LHCb experiment Proton-proton interactions at √s = 14 TeV at LHC • Particle ID • needed between • 1-150 GeV/c • Two RICH • systems with • 3 Cherenkov • radiators • Acceptance: • 10-300 mrad • (bending plane) • 10-250 mrad • (non-bending plane) RICH1 RICH2 Local Luminosity 2 x 1032 cm-2s-1

  3. Momentum LHCb RICHes detectors RICH2 RICH1 m RICH1

  4. Aerogel as Cherenkov radiator • Light, solid quartz-like structure SiO2 • Physical properties: low density,r = 0.15 g/cm³ • n = 1.01 ÷ 1.10, • (n = 1 + 0.20r) Novosibirsk tile 10x10 cm² tile 7x8 cm² tile1 + tile2 • Aerogel type : • Novosibirsk, Boreskov Institute • of Catalysis, Russia (hygroscopic) • SP30 Matsushita Electric works Ldt, • Japan (hydrophobic) 8cm T = A e-Cd/ l4 Ais the long l transmittance Cis the clarity coefficient A = 95.88 ± 0.04, C = (6.44 ± 0.01) 10ˉ³ μm¯4 /cm A = 91.97 ± 0.05, C = (7.22 ± 0.01) 10ˉ³ μm¯4 /cm A = 88.18 ± 0.06, C = (6.95 ± 0.01) 10ˉ³ μm¯4 /cm

  5. Ageing tests with γ 60Co (Eg = 1.3 MeV, 1.7 MeV) Dose : 420 rad/min

  6. Ageing tests with protons 1 year LHCb operation 13 Source of radiation: Protonbeam 24 GeV/c Flux : 9 109 p/cm2/s Spot size : 2 x 2 cm2 Depletion in Transmittance of ~1% after 1 year run (w.r.t. non irradiated sample taken as a reference)

  7. Humidity tests Expose hygroscopic aerogel tile to humid air (70%) Measure water absorption through weight MeasureTransmittance in range 200-800 nm Loss of 30% at 300 nm Loss of 15% at 400 nm Loss of 8% at 500 nm

  8. Test beam Set-up at CERN Beam from CERN-PS:πˉandp/πin the range 6 – 10GeV/c (Δp/p = 1%)

  9. Bialkali photocathode, K2CsSb • Fountain shaped electric field, • demagnification factor ≈ 2.3 • Silicon pad sensor 2048 pixels • (16 sectors x 128 pads 1x1 mm² • 2.3x2.3 mm² granularity on ph.cathode) Hybrid Photo Detectors AEROGEL test beam Quantum Efficiencyof the 4 photocathodes > 20% (l=280-380nm)

  10. Monte Carlo description All relevant processes are considered in the simulation: Photo Detectors • Rayleigh scattering • Refraction on the boundaries • Light absorption • Light detection on photocathode • Photocathode transparency... Aerogeltile Mirror Geant4 Endcap Silicon layers photons Beam axis Aerogel Glass filter Place holder

  11. Test beam results • 9 Gev/c π¯ beam • 4 cm aerogel Novosibirsk • noise/pad < 2% Ring region sect 8 Sector #4 sect 4 Out of ring Sector #8

  12. Photoelectron yield • Integrate signal across the measured • arcs and compare with Monte Carlo • Evaluate nr. photoelectrons: • - on ring, |R-R| < 3σ • - out of Cherenkov ring Novosibirsk 4 cm aerogel 8 cm aerogel On ring Number of ph.electrons

  13. Photoelectron yield cont’d on-ring D263 No filter Data 4 cm MC 8 cm results are normalised to 2π acceptance off-ring results are in units of 10¯²/cm² 4 cm • Contributions to total error: • background subtraction (±1σ): ~ 5% • inefficient or noisy pads : ~ 4% • definition of ‘active region’ (±1mm): 2% • separation of on-ring/off-ring (±2mm): 3% • signal losses outside ADC thresholds (±1σ): 3% 8 cm Npe

  14. Ring reconstruction -- Data -- Monte Carlo 4cm Novosibirsk (no filter) • Study resolution as a function of • - filter type • - aerogel thickness • - aerogel type • Results per single photoelectron are (mrad): θc rad Data MC Novosibirsk Data Matsushita

  15. Ring reconstruction cont’d -- Fit to data • Resolution is expected to scale as • A/√N + k (in the 3σ ring region) • Contribution to angular resolution • is determined with the simulation: Resolutions differ by ~20-40% in MC with respect to the Data. Still under investigation.

  16. PID performance SINGLE ph.e. 6.1s 6 GeV p/pseparation at 8 GeV ~30,000 events 4.8s 8 GeV 3.1s 10 GeV θ rad

  17. PID performance cont’d • Evaluate separations Nσ = Δθ/σθ, scaling with • the Npe and extrapolate to the total acceptance • For 4 cm aerogel + filter: π-ring p-ring Clear π/p separation

  18. Conclusion • The use of aerogel as Cherenkov radiator has become reliable in high energy particle physics • Test beam has shown a photon yield which agrees with the Monte Carlo expectations • Good PID ability in the momentum range 6 – 10 GeV/c • Further studies are on the way

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