rich1 @ cbm serguei sadovsky ihep, protvino cbm meeting gsi, 12 february 2004
TRANSCRIPT
RICH1 @ CBMRICH1 @ CBM
Serguei SadovskyIHEP, Protvino
CBM meetingGSI, 12 February 2004
B
MC
Outline
General scheme of the detector Optics Photo-detector Small diameter PMT HV regulation GEANT3 simulation UrQMD events GEANT4 simulation Conclusion
B
MC
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
B
MC
Optical scheme of the RICH1 detector
Vertical Horizontal
V.Khmelnikov
B
MC
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
B
MC
One (upper) array of the hexagonal Be-glass mirrors
B
MC
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
B
MC
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: 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
V.Rykalin, R.Sidoreev
B
MC
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
MC
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
B
MC
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 [email protected]
B
MC
G3: one particle response, N2
Number of Cherenkov photons focused onto the photodetector plane emitted by one electron of charged pion
B
MC
G3: one particle response, CH4
B
MC
G3: one particle response, C4H10
B
MC
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
MC
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
MC
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.
B
MC
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
B
MC
G3: Electron/position vertices
N2 CH4
RICH wall
target
RICH mirror
B
MC
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
B
MC
G3: tracks in heavy-ion collisions, CH4
Primary tracks Primary+secondary tracks
B
MC
G3: ring images in heavy-ion collisions, N2
Primary tracks Primary+secondary tracks
B
MC
G3: ring images in heavy-ion collisions, CH4
Primary tracks Primary+secondary tracks
B
MC
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
MC
GEANT4 model
Boris Polichtchouk([email protected])
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
MC
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
MC
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
MC
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
MC
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
MC
G4: RICHHits
RICHHit class was implemented
At the moment we need Position, Momentum and TOF information to be stored in RICHHits and saved.
B
MC
3 GeV electron in N2 radiator
GEANT4
RICH1
B
MC
G4: electron on the focal plane
B
MC
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