CBM RICH

1
CBM RICH

• Serguei Sadovsky
• IHEP, Protvino
• CBM-Russian meeting
• ITEP, 5 November 2004

2
Outline

• Conceptual design of RICH
• Optics and Be-glass mirrors
• Radiator gases
• Small diameter PMT FEU-Hive
• Inputs for RICH FEE
• Simulation results
• Summary 2004
• Plans for 2005 and beyond

3
Conceptual design of RICH1

• 2.2-m long gas radiator with 40He60CH4, pure
  N2 or 60N240CH4 gas mixture
• Two identical walls of the hexagonal spherical
  Be-glass mirros
• Two photo-detector planes with aperture 3x0.6 m2
  each on the base of PMT FEU-Hive
• Support structure for photo-detector planes and
  mirror walls
• Gas vessel with beam pipe in the center and gas
  supply system

4
Optical scheme of the RICH1 detector
V.Khmelnikov
Vertical
Horizontal
5
Be-glass mirrors, production details

• Curvature radius of the mirror surface is 450 cm
• The maximal size of the Be hexagons is 60 cm
• Mirror thickness is 3 mm of Be and 0.5 mm of
  glass,
• i.e. in total 1.25 of X0
• The weight of one
• hexagon is 1.3 kg

heater
High temperature (600?C)
beryllium
glass
6
Be-mirror prototype without Al covering for LHCb
experiment, photo
7
Be-mirror prototype, optics quality measurements

• Angle deviation from the nominal value s?0.03
  mrad
• Image diameter of a point sours (95 of the
  sours intensity) D00.4 mm
• The optical surface roughness sh of mirror is 1.6
  nm after the glass polishing, Al covering and
  SiO2 coating

8
Be-mirror reflectivity in dependence on photon
wave length

• The optical surface roughness s of mirror is 1.6
  nm
• Total reflectivity R0 of mirrors with Al
  coverage is 92
• Specular reflectivity
• Rsp R0exp(-4?s/?)
• and defuse reflectivity
• Rdf R0-Rsp

A.Braen M.Kostrikov, Preprint IHEP 93-129
9
Upper wall of the hexagonal Be-glass mirrors in
terms of hexagons, aperture is 4.5x1.75m2
10
Be-mirror wall, optics simulation
Claudia Höhne

• rings(q,f) - q polar angle,
• f azimuth angle
• no diffusion at reflection
• no magnetic field, no multiple scattering

Simulation result Optics distortions
(eccentricity) for large q,f To do improve
optics of the mirror walls / focussing position
of focal planes
11
Be-mirror wall, optics simulation (2)
Claudia Höhne
Electron rings after the photo-detector plane
tilding Focussing is perfect now Sperical
abberation is still clearly seen
12
Radiator gases, properties
N2 60 N240CH4
40He60CH4 n 1.000298
1.000356 1.0002804 gth 41
37.5 42.24 pp,th 5.72 GeV/c 5.25
GeV/c 5.9 GeV/c Qc
1.398o 1.53o 1.36o X0 304 m 386
m 999 m
Dispersion of refractive index
N2 A29.06 10-5 B7.7 10-3 He A3.48 10-5 B2.3
10-3 CH4 A42.6 10-5 B12.0 10-3
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Radiator gases, transmittances
N2
CH4
Y.Tomkiewicz and E.L.Garwin, NIM V114 (1974) pp.
413-416
L.Fabbietti for HADES, NIM A 502 (2003) 256
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Photo-detector plane

• Hexagonal packing of the small diameter PMT
  FEU-Hive with glass cathode window
• P-terphenyl WLS film for detection of 100 - 330
  nm ultraviolet photons
• Improvement of the photon collection by special
  Al foil inserts

15

16
Yuri Kharlov
Aperture optimization of the Photo-detector
plane
UrQMD
PLUTO
17
The PMT FEU-Hive as the UV detector

• The PMT FEU-Hive has been designed in
  cooperation of IHEP with the Moscow Electrolamp
  Company (MELZ) on a base of the resistive
  distributed dynode system with electrostatic
  focusing, bialkaline photo-cathode and tube with
  a glass window.
• The electrostatic optics, construction details
  and PMT parameters have been optimized by using
  computer model of the PMT.
• By means of the optics and dinode system
  optization one achieves effective operation of
  the PMT in one-photo-electron regime, which is
  important for application in RICH detectors.

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Parameters of the PMT FEU-Hive
V.Rykalin, R.Sidoreev rykalin_at_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 25
• Effective number of dynodes is 12
• Nominal HV is less than 2 kV
• Amplification is 106
• Dynamical charge range is 0.25-2.5 pC
• Noise current is 3000 e/sec
• Capacitance is 15 pF
• Power dissipations is 40 mW
• Price is less than 25 Euro/PMT

19
PMT FEU-Hive, quantum efficiency
FEU-Hive, Radiant sensitivity
PT WLS
Well know properties of the bialkaline
photocathode
Prediction, based on the previous measurements
20
Properties of the PT WLS
21
PMT FEU-Hive, simulation results
Photons/PMT in UrQMD
One photoelectron spectrum
Pulse jitter
22
Inputs for RICH Front End Electronics
V.Leontiev, M.Bogolyubsky

• on the base of the PMT FEU-Hive
• Negative polarity of the output signals
• Total charge in a pulse from 0.25 to 25 pC
• Noise -- 3000 e/sec
• Pulse lenght -- several ns
• Output capasitance -- 15 pF
• ADC bit number -- 8-9 bits
• Channel density -- 2.5 channels /cm2
• Total number of channels 60000-120000
• There is a limitation on the total power
  consumption of RICH electronics placed in gas
  vessel

23
HV regulation
V.Leontiev, M.Bogolyubsky

• Classical scheme of the HV regulation with
  ballast resistor and PMT dividing sercuit
• The ballast resistor has 6 bit regulation in the
  region 1.6-2 kV, i.e. with 6V step
• Do we really need such fine HV regulation?
• This is question to the production technology
  ...
• and avaliable space, we have only 0.4
  cm2/channel

24
RICH simulation
Claudia Höhne Yuri Kharlov Boris Polishchuk
CbmDetector
CbmTask
CbmRich
CbmRichHitProducer
CbmRichRingGuidanceProducer
CbmRichRingFinder
CbmRichPoint
CbmRichHit
CbmRichMirrorPoint
CbmRichRingGuidances
CbmRichRing
CbmMCPoint
CbmHit
TObject
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RICH in CBMroot
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Single particle response photon Numb
50N250CH4
40He60CH4
N2
27
Single particle response ring radiuses
50N250CH4
40He60CH4
N2
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Ring multiplicity in Au-Au collisions
40He60CH4 37 rings 50N250CH4 39 rings N2
41 rings
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Detector occupancy in Au-Au collisions

• On average 700-900 fired PMT per central event
• Not taken into account yet
• noise
• diffusive reflection
• possible gas fluorescence

30
MC points hits rings
y cm
Photo-detector plane 1 central AuAu collision,
25 AGeV (UrQMD) hits rings (primary vertex
tracks)
ring center guidances ( extrapolation of
charged tracks from primary vertex)
x cm
31
Electron rings tracks matching efficiency
Boris Polishchuk
s(R)/R0.04
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Summary 2004

• Conceptual design of RICH1 is ready
• Realistic CBMroot model of RICH1 has been
  written, but further development is still needed
• There are 3 options of gas radiator N2,
  60N240CH4 and 40He60CH4, we have to choose
  the optimal one
• The gas radiator option is essential for design
  of the gas vessel and gas supply system of RICH1
• Be-glass mirrors are chosen as the main option,
  several mirror prototypes has been produced for
  LHCb, but the mirror prototype for the CBM
  experiment is also needed
• Small diameter PMT FEU-Hive is proposed as main
  option for the UV photo-detector
• Computer model of the PMT FEU-hive exists,
  construction optimization has been performed,
  prototyping is the next step
• The first version of the ring reconstruction is
  written
• Electron rings and tracks matching has been
  performed

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Plans for 2005

• Production and test of the PT WLS film prototypes
  
• for CBM RICH
• Tests of the gas radiators (N2, 60N240CH4,
  40He60CH4) at the secondary beams of the U70
  accelerator of IHEP with the aim to choose the
  optimal gas radiator
• Production of the first several PMT FEU-Hive and
  measurement of their basic properties
• RICH optics tuning
• Photo-detector plane aperture choosing
• Further development of the RICH simulation model

34
and beyond

• Design, production and beam test of the RICH
• prototype which will include
• Be-glass hexagonal mirror with external diameter
• of 60 cm and the radius of curvature of 450
  cm
• Gas vessel as 2.2 m long tube with diameter
• of 70 cm
• Photo-detector plane assembled with 600 PMT
  FEU-Hive and WLS films on the photo-cathode
  windows
• Relevant electronics

35
IHEP experience in RICH, the first detector
The first measured ring radius distribution
The first in the word RICH on the base of 12
hodoscope PMT produced in IHEP, B. Baldin et al.
1974
Further development, SKOC, 1983
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IHEP experience in RICH detector development

• RICH with 12 hodoscope PMT, produced in IHEP
  .. 1973
• RICH with 144 PMT.. 1977
• RICH (SKOC) for FODS experiment with
• 24 hodoscope PMT, produced in IHEP
  .... 1983
• RICH with 320 small size PMT for SPHINX
• experiment in IHEP ..1984
• RICH with the WLS films on photo-cathode windows
• for SELEX experiment in FNAL
  ....1996
• RICH for OKA experiment in IHEP 200?