CBM Serguei Sadovsky IHEP, Protvino CBM meeting GSI, 12 February 2004

B M C Outline General scheme of the detector Optics Photo-detector Small diameter PMT HV regulation GEANT3 simulation UrQMD events GEANT4 simulation Conclusion

B M C General scheme of RICH1 2.2-m long gas radiator with N 2, CH 4 and C 2 H 10 gas mixture Two arrays of the hexagonal spherical Be- glass mirros Two photodetector planes And corresponding support infrastructure

B M C Optical scheme of the RICH1 detector Vertical Horizontal V.Khmelnikov

B M C 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 X 0 The size of the Be hexagons is 60 cm The weight of one hexagon is 1.3 kg

B M C One (upper) array of the hexagonal Be-glass mirrors

B M C Photo-detector plane Hexagonal packing of small diameter PMT with cone-shaped reflectors WLS films for detection of nm ultraviolet photons The effective detection region for Cherenkov photons is nm

B M C Small diameter IHEP-MELZ FEU-XXX External PMT diameter is 6 mm Photo-cathode diameter is 5 mm PMT length is 60 mm Photo-cathode: K 2 CsSb Quantum efficiency at 410 nm is 20% Effective number of dynodes is 12 Nominal HV is less than 2 kV Amplification is more than 10 6 Preamplifier is, probably, needed Price is less than 25 Euro/PMT V.Rykalin, R.Sidoreev

B M C 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. V.Leontiev, M.Bogolyubsky

B M C 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 A Maximum dissipation power is 200 mW Step of the HV regulation is 6.5 V

B M C GEANT3 model 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 Yuri Kharlov

B M C G3: one particle response, N 2 Number of Cherenkov photons focused onto the photodetector plane emitted by one electron of charged pion

B M C G3: one particle response, CH 4

B M C G3: one particle response, C 4 H 10

B M C 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  -electrons, emit Cherenkov photons (see 1-particle response)

B M C 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

B M C G3: Cherenkov photon multiplicity in heavy-ion collisions, N 2 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.

B M C G3: Cherenkov photon multiplicity in heavy-ion collisions, CH 4 Primary tracks give about 2500 Cherenkov photons All tracks (primary+secondary) give about 4000 photons. The Al wall thickness is 0.5 mm

B M C G3: Electron/position vertices N2N2 CH 4 RICH wall target RICH mirror

B M C G3: tracks in heavy-ion collisions, N 2 Number of tracks per event emitted Cherenkov photons focused onto the photo-detector plane Primary tracksPrimary+secondary tracks

B M C G3: tracks in heavy-ion collisions, CH 4 Primary tracksPrimary+secondary tracks

B M C G3: ring images in heavy-ion collisions, N 2 Primary tracksPrimary+secondary tracks

B M C G3: ring images in heavy-ion collisions, CH 4 Primary tracksPrimary+secondary tracks

B M C 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

B M C GEANT4 model Boris Polichtchouk 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)

B M C 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

B M C 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

B M C 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.

B M C 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.

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

B M C 3 GeV electron in N 2 radiator GEANT4 RICH1

B M C G4: electron on the focal plane

B M C 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 (N 2 or CH 4 ) 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