Photon Detection Efficiency in the CsIbased HADES RICH

1
Photon Detection Efficiency in the CsI-based
HADES RICH

• Description of the HADES RICH
• OEM Measurement
• Single Photon Response
• N0 Calculation
• Summary

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The RICH Detector
C C _at_1 AGeV
Lepton Rings

• Photon Detector
• CH4 MWPC
• CsI cathode
• 28.600 pads
• 10 ms readout

Single Photon Response is CRUCIAL
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Efficiency Calibration(Online Efficiency
Measurement (OEM))
Calibrated light source !

• Photons produced by 600 AMeV 12C beam particles
  passing two different solid radiators

n(l) -gt QC(l)
1 0.8 0.6 0.4 0.2 0.0
SiO2 MgF2
Transmission
120 140 160 180 200 220
l nm
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OEM Radiator
beam
beam line
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Single Particle Response
Nph N0 Z2
100 evt accumulated
SiO2
MgF2
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Single Photon Response of MWPC
wires
1 Event
Pulse Height
Pad Y Coordinate
6 mm
6 mm
Pad X Coordinate
Q Mean 7 10 4 e- eSE 90

• Photon Candidates Local Maxima in an isolated
  3X3 Pattern
• Single Pads below Threshold (4 s) and Charge
  Particle are cleaned

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Coupling to Neighbouring Pads
Along the wire ? photon impact
resolution 0.5 mm
Perpendicular to wire
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Charge Distribution of Single Photons
Simulation
Experiment
single photon response well understood
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OEM Analysis
Experimental Data
Simulation Input (HGeant)
C_at_600 AMeV
N0102
100 Events
Beam pipe shadow

• Optical parameters (all independently
  measured)
• Simulation of single photon response
• Electronic noise

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Wave Length Resolved Efficiency
Simulation Experiment
Sector 2
MgF2 Radiator
SIO2 Radiator
MgF2
SiO2
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N0 Calculation
Translation to HADES C4F10 Radiator
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N0 Results
Experimental Results extracted from the April
2002 data C _at_ 600 AMeV
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Conclusions and Outlook

• We have developed a powerful online efficiency
  measurement for the HADES Rich detector.
• The analysis of the single photon response has
  allowed to develop an heuristic model for the
  simulations.
• The quantitative comparison between experimental
  and simulated data enables an estimation of the
  figure of merit N0 for each sector of the HADES
  RICH detector.
• The OEM measurement is going to be repeated
  during the next experiment, to monitor the time
  evolution of the detector efficiency.

Munich RICH group T.Christ, T.Eberl,
L.Fabbietti, J.Friese, R. Gernhaeuser, L.Maier,
B.Sailer and S.Winkler.
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Pulse Height Distribution
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