Concept for a RICH detector for the CBM experiment at the future accelerator facility FAIR at GSI in Darmstadt

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Concept for a RICH detector for the CBM
experiment at the future accelerator facility
FAIR at GSI in Darmstadt
Claudia Höhne - GSI Darmstadt, Germany CBM
collaboration
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Outline

• context of the RICH detector
• CBM _at_ FAIR
• CBM physics
• requirements for RICH detector
• design of RICH detector
• mirrors
• photodetector
• radiator
• simulations
• summary - outlook - future plans

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CBM _at_ FAIR

• Facility for Antiproton and Ion Research
• next generation accelerator facility
• double-ring synchrotron
• simultanous, high quality, intense primary and
  secondary beams
• cooler/ storage rings (CR, NESR, HESR)

Cooled antiproton beam hadron spectroscopy
Ion and Laser induced plasmas High energy
density in matter
Structure of nuclei far from stability
Compressed Baryonic Matter
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CBM physics
Investigation of the phase diagram of strongly
interacting matter
lattice QCD Fodor / Katz, Nucl. Phys. A 715
(2003) 319

• high T, low mB
• ? top SPS, RHIC, LHC
• low T, high mB
• ? SIS
• intermediate range ?
• ? low energy runs SPS, AGS
• ? SIS 300 _at_ GSI !
• Critical point?
• Deconfinement?
• Highest baryon densities
• ? in medium properties of hadrons (r, w, f),
  restoration of chiral symmetry?

dense baryonic medium
dilute hadron gas
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CBM experiment
Compressed Baryonic Matter experiment

• tracking, vertex reconstruction radiation hard
  silicon pixel/strip detectors (STS) in a magnetic
  dipole field
• electron ID RICH TRD ( ECAL) ? p
  suppression ? 104

• hadron ID TOF ( RICH)
• photons, p0, m ECAL
• high speed DAQ and trigger

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RICH detector in CBM
task of RICH detector

• precise measurement of ee- pairs from the decay
  of r, w, f mesons within a large acceptance
  (p-suppression 10-410-3)
• improve p/K separation at higher momenta
• (kaon ID by TOF quickly deteriorates above 4
  GeV/c)

detector requirements

• radiator with high threshold (gth gt 40)
• ? pp,th 5-6 GeV/c, 90 of qe reached at 12-13
  GeV/c
• sufficient radiator length for generation of
  Cherenkov photons (Ng gtgt 10), small radiation
  length, good UV transparency of radiator gas
• low material budget (holds for all detector
  parts) to minimize secondary interactions and in
  particular ee- pairs from g-conversion
• large, continuous mirror-surface with excellent
  optical properties
• fast photodetectors (107 Hz) with wide detection
  range, high qe, high granularity

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RICH design

• 2.2m long gas radiator
• gas vessel with beam pipe in the center
• 2 mirror and 2 photo-detector planes (vertically
  separated)
• mirror Beglass, R450cm
• 2 x (450cm x 175cm)
• photo-detector PMT plane
• shielded by magnet yoke
• 2 x (280cm x 140cm)
• support structures preferably from side

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RICH mirror (IHEP Protvino, Russia)

• spherical mirror, R450cm
• Be hexagons (3mm thick, maximum diameter 60cm,
  1.3kg) covered with 0.5mm glass
• ? 1.25 of X0
• glass polishing, Al covering, SiO2 coating ? 92
  total reflectivity in wide wavelength range
• excellent optics, no degradation and radiator
  gas pollution due to long exposition in a
  radiation hard environment expected

production assembly
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RICH mirror

• prototype available
• optical surface roughness sh 1.6nm (after
  glass polishing, Al covering and SiO2 coating)
• ? diffuse reflection of only 12 of total for l
  150nm
• image diameter of a point source D0 0.4mm
  (contains 95 of reflected light)
• ? angular deviation from nominal curvature sq
  0.03mrad

Be plate for LHCb Be-mirror prototype
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PMTs (IHEP Protvino Moscow Electrolamp)

• PMT FEU-Hive
• K2CsSb photo-cathode, 25 quantum efficiency at
  l 410nm
• to be covered with transparanet WLF film
  (p-theraphenyl) ? 22 qe for wide range
• 90 geometrical efficiency

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PMT FEU-Hive

• external PMT diameter 6mm
• photo-cathode diameter 5mm
• ? 105 channels per detector plane
• length 6cm
• high voltage 2kV
• effective number of dynodes 12
• amplification 106
• ? effective operation in one-photoelectron regime
• power dissipation 40mW
• noise current 3000 e-/s
• capacitance 10-15 pF
• dynamical range of signal charge
• Q (0.25-25) 106 e-
• average signal time 1ns

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radiator

• no window between radiator and photo-detectors
  He, N2, CH4
• fluorescence? CH4 as quenching gas in mixture?
• gth gt 40, UV transmittance, radiation length!
• ideal would be an easy handling (gas system)

n gth qc pp,th
lth X0 He 1.000035 119.5 0.48 16.7
GeV/c 50nm 5300m N2 1.000298
41 1.4 5.72 GeV/c 80nm
304m CH4 1.000444 33.6 1.7 4.68
GeV/c 145nm 650m 60N2
40CH4 1.000356 37.5 1.53 5.25
GeV/c 145nm 386m 40He
60CH4 1.0002804 42.2 1.36 5.9
GeV/c 145nm 999m
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Simulation (GEANT3)

• CBM detector simulation framework
• GEANT 3, GEANT 4
• implementation of RICH detector
• Cherenkov properties of materials from HADES,
  literature

beam

• study basic properties of current detector
  concept
• prove feasibility of desired p-suppression
• optimize geometrical design, optical layout

Gasbox 250 mm aluminum
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Imaging properties of mirror

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

optimize optical design of detector!
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Single particles

• e/p separation (depending on radiator) up to
  11-14 GeV/c
• p identification from 5-7 GeV/c to 11-14 GeV/c
• diameter of ring 10.6-12 cm 17-20 PMTs
• wide acceptance covered

single e- acceptance
radiator 40He60CH4
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figure of merit
Cherenkov spectrum for N2
40He 60CH4 lmin Ng N0 cm-1
NPMT 120nm 33 292 25 200nm 23 204
18 250nm 15 138
11 300nm 11 93 8
Ng 1.3 NPMT
Importance of continuation of the development of
PMTs with large qe in the UV range!
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UrQMD event
35 AGeV central AuAu

• about 40 rings/event
• 33 electrons (13 from primary vertex)
• 7 pions
• 0.1 muons

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UrQMD event
35 AGeV central AuAu

• z-coordinates of track vertices for particles
  detected in RICH
• target (z 0cm) - 125mm Au
• 7 STS 2x100mm, 5x200mm Si
• (z 5,10,20,40,60,80,100 cm)
• beampipe (z 20-30 cm)
• magnet yoke (z 110-140 cm)

optimize CBM detector layout to further suppress
ee- pairs from g-conversion!
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p misidentification

• first estimation
• assume 100 ring finding, match closest track to
  a certain ring
• large number of charged tracks per event,
  additional information available from TRD, TOF

ideal tracking
1 momentum resolution
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summary - outlook - future plans
concept of RICH detector for the CBM experiment
introduced
optimize detector layout (optics
system!) continue RICH RD (radiator, mirror, PMT)
2006/2007 RICH prototype 2006/2007 2007/2008 beam
tests of RICH prototype 2007/2008 2008/2009 final
RICH design 2009/2010 RICH production -
2012 installation, commissioning, beam!