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RICH1 @ CBM

RICH1 @ CBM. Serguei Sadovsky IHEP, Protvino CBM meeting GSI, 12 February 2004. Outline. General scheme of the detector Optics Photo-detector Small diameter PMT HV regulation GEANT3 simulation UrQMD events GEANT4 simulation Conclusion. General scheme of RICH1.

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RICH1 @ CBM

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  1. RICH1 @ CBM Serguei Sadovsky IHEP, Protvino CBM meeting GSI, 12 February 2004

  2. Outline • General scheme of the detector • Optics • Photo-detector • Small diameter PMT • HV regulation • GEANT3 simulation • UrQMD events • GEANT4 simulation • Conclusion

  3. General scheme of RICH1 • 2.2-m long gas radiator with N2, CH4 and C2H10 gas mixture • Two arrays of the hexagonal spherical Be-glass mirros • Two photodetector planes • And corresponding support infrastructure

  4. Optical scheme of the RICH1 detector V.Khmelnikov Vertical Horizontal

  5. Mirror parameters • Two identical mirror planes tilted by 12º in the vertical plane • The surface curvature radius is 450 cm • Mirror thickness is 3 mm Be and 0.5 mm glass, i.e. in total 1.25% of X0 • The size of the Be hexagons is 60 cm • The weight of one hexagon is 1.3 kg

  6. One (upper) array of the hexagonal Be-glass mirrors

  7. Photo-detector plane • Hexagonal packing of small diameter PMT with cone-shaped reflectors • WLS films for detection of 150 - 330 nm ultraviolet photons • The effective detection region for Cherenkov photons is 150 - 600 nm

  8. Small diameter IHEP-MELZ FEU-XXX V.Rykalin, R.Sidoreev rykalin@mx.ihep.su • External PMT diameter is 6 mm • Photo-cathode diameter is 5 mm • PMT length is 60 mm • Photo-cathode: K2CsSb • Quantum efficiency at 410 nm is 20% • Effective number of dynodes is 12 • Nominal HV is less than 2 kV • Amplification is more than 106 • Preamplifier is, probably, needed • Price is less than 25 Euro/PMT

  9. V.Leontiev, M.Bogolyubsky HV regulation • Classical scheme of the HV regulation with ballast resistor and PMT dividing sercuit • The ballast resistor has 6 bit regulation • Commutation scheme is shown in the Fig.

  10. HV commutation parameters Optopair KP4010 of the COSMO firm will be used for the HV commutation. The main parameters: • Isolating voltage is 400 V (max. 500 V) • Maximum dark current is 10-6 A • Maximum dissipation power is 200 mW • Step of the HV regulation is 6.5 V

  11. GEANT3 model Yuri Kharlov Yuri.Kharlov@ihep.ru • We start from GEANT3 simulation because it is a stable tool verified by 30-year experience. • The present detector model is simplified as much as possible: • Magnet with homogeneous field of 1 Tm • RICH filled by a gas without light attenuation • The detector wall is 0.5 mm of Al • Spherical mirror with 100% reflectivity • Photo-detector sensitive plane with 100% detection efficiency

  12. G3: one particle response, N2 Number of Cherenkov photons focused onto the photodetector plane emitted by one electron of charged pion

  13. G3: one particle response, CH4

  14. G3: one particle response, C4H10

  15. RICH1 in heavy-ion collisions with UrQMD model • Central Au+Au collisions at 30 GeV/u, b<3 fm were simulated in UrQMD 1.3 • Generated events were tracked by GEANT3 code • Charged hadrons give Cherenkov light at high energies only, while any electrons, even d-electrons, emit Cherenkov photons (see 1-particle response)

  16. G3: One UrQMD event Energy cut – 20 MeV pink – Cherenkov photons red – charged hadrons blue – high-energy photons green – electrons yellow – muons black – neutral hadrons

  17. G3: Cherenkov photon multiplicity in heavy-ion collisions, N2 Primary tracks give about 1500 Cherenkov photons focused onto the photo-detector plane. All tracks (primary+secondary) give about 2000 photons. Cherenkov photons are mainly due to secondary electrons/positions. The Al wall thickness is 0.5 mm.

  18. G3: Cherenkov photon multiplicity in heavy-ion collisions, CH4 Primary tracks give about 2500 Cherenkov photons All tracks (primary+secondary) give about 4000 photons. The Al wall thickness is 0.5 mm

  19. G3: Electron/position vertices N2 CH4 RICH mirror target RICH wall

  20. G3: tracks in heavy-ion collisions, N2 Number of tracks per event emitted Cherenkov photons focused onto the photo-detector plane Primary tracks Primary+secondary tracks

  21. G3: tracks in heavy-ion collisions, CH4 Primary tracks Primary+secondary tracks

  22. G3: ring images in heavy-ion collisions, N2 Primary tracks Primary+secondary tracks

  23. G3: ring images in heavy-ion collisions, CH4 Primary tracks Primary+secondary tracks

  24. G3: ring images in heavy-ion collisions, discussion The central region of the photo-detector plane is too cloudy by Cherenkov photons. As possible solutions of the problem we can propose: • to use the smaller diameter PMTs in this region for reduction of the PMT occupancy • to use 8-bit ADC for measurements of Cherenkov photon multiplicities in the central PMTs

  25. GEANT4 model Boris Polichtchouk (Boris.Polichtchouk@cern.ch) • Simple and idealized geometry, just to test the functionality, however all other CBM detectors are switched on in G4CBM framework • Basic classes and functionality implemented (Cherenkov light, optical photons tracking, optical surfaces)

  26. G4: Geometry features • Spherical mirror R=450 cm, 100% reflectivity • Sensitive focal plane (RICHSensitiveDetector), 100% efficiency of optical photons detection • Gas radiator without light attenuation

  27. G4: Geometry Construction • Using of GlobalGeometryReader as much as possible • Shapes, rotation matrices, sensitive volume flags are read from GEOM/RICH/.. • Optical properties of the radiator gas, mirror and sensitive volumes are implemented in RICHDetectorConstruction::Construct() method

  28. G4: Physics • CBMPhysicsList was extended to comprise the physics of Cerenkov photons • Optical photon physics was implemented in the OpPhysics class and added to CBMPhysicsList.

  29. G4: Tracking • 50 MeV default cut is good for particle zoo but not fine for Cherenkov photons tracking! • So, RICHTrackingAction class was implemented.. • ..and GlobalTrackingAction was slightly corrected to allow for optical photons tracking.

  30. G4: RICHHits • RICHHit class was implemented • At the moment we need Position, Momentum and TOF information to be stored in RICHHits and saved.

  31. GEANT4 RICH1 3 GeV electron in N2 radiator

  32. G4: electron on the focal plane

  33. Summary • RICH1 conceptual design is presented, including: • General detector schematics layout and optics • The first Be-glass mirror design • Photo-detector plane based on small-diameter PMT with WLS • Scheme of the PMT HV regulation • GEANT3: • Light gas (N2 or CH4) is needed to cut charged pions by the Cherenkov threshold • Low material budget is necessary to prevent from secondary electrons production in detector media • High granularity of photo-detector with amplitude measurement in the central region is desired to reconstruct ring images • GEANT4: • RICH1 basic functionality was implemented in G4CBM simulation framework • ..but a lot of work is still needed to make a detailed physics simulation! • RICH1 simulation is in progress, G3 and G4 in parallel

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