rich1 @ cbm serguei sadovsky ihep, protvino cbm meeting gsi, 12 february 2004

RICH1 @ CBMRICH1 @ CBM

Serguei SadovskyIHEP, Protvino

CBM meetingGSI, 12 February 2004

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Outline

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

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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

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Optical scheme of the RICH1 detector

Vertical Horizontal

V.Khmelnikov

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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

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

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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

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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

rykalin@mx.ihep.su

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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

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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

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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 KharlovYuri.Kharlov@ihep.ru

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G3: one particle response, N2

Number of Cherenkov photons focused onto the photodetector plane emitted by one electron of charged pion

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G3: one particle response, CH4

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G3: one particle response, C4H10

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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)

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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

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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.

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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

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G3: Electron/position vertices

N2 CH4

RICH wall

target

RICH mirror

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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

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G3: tracks in heavy-ion collisions, CH4

Primary tracks Primary+secondary tracks

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G3: ring images in heavy-ion collisions, N2

Primary tracks Primary+secondary tracks

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G3: ring images in heavy-ion collisions, CH4

Primary tracks Primary+secondary tracks

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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

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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)

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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

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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

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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.

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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.

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G4: RICHHits

RICHHit class was implemented

At the moment we need Position, Momentum and TOF information to be stored in RICHHits and saved.

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3 GeV electron in N2 radiator

GEANT4

RICH1

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G4: electron on the focal plane

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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