1. Photon Detection Efficiency in the CsI-based HADES RICH
Description of the HADES RICH
OEM Measurement
Single Photon Response
N0 Calculation
Summary
L. Fabbietti (TU-München)

2. Single Photon Response is CRUCIAL
The RICH Detector
C + AGeV
Lepton Rings
Photon Detector :
CH4 MWPC
CsI cathode
pads
10 ms readout
Single Photon Response is CRUCIAL
L. Fabbietti (TU-München)

3. Efficiency Calibration (Online Efficiency Measurement (OEM))
Calibrated light source !
Photons produced by 600 AMeV 12C beam particles passing two different solid radiators
n(l) -> QC(l) 1
0.8
0.6
0.4
0.2
0.0
SiO2
MgF2
Transmission
l [nm]
L. Fabbietti (TU-München)

4. OEM Radiator
beam
beam line
2cm
L. Fabbietti (TU-München)

5. Single Particle Response
Nph ~ N0 * Z2
100 evt accumulated
single 12C hit
beam pipe shadow
SiO2
MgF2
L. Fabbietti (TU-München)

6. Single Photon Response of MWPC
wires
1 Event
Single Photon
Pattern
Pad Y Coordinate
Pulse Height
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
L. Fabbietti (TU-München)

7. Coupling to Neighbouring Pads
Along the wire
 photon impact resolution ~ 0.5 mm
Perpendicular to wire
L. Fabbietti (TU-München)

8. Charge Distribution of Single Photons
Simulation
Experiment
single photon response
well understood
L. Fabbietti (TU-München)

9. Simulation Input (HGeant)
OEM Analysis
Experimental Data
Simulation Input (HGeant)
AMeV
100 Events
N0=102
Beam pipe shadow
Optical parameters (all independently measured)
Simulation of single photon response
Electronic noise
L. Fabbietti (TU-München)

10. Wave Length Resolved Efficiency
Simulation
Experiment
Sector 2
MgF2
Radiator
150 nm
205 nm
145 nm
163 nm
SIO2 Radiator
MgF2
SiO2
Q l
L. Fabbietti (TU-München)

11. N0 Calculation Translation to HADES C4F10 Radiator
L. Fabbietti (TU-München)

12. N0 Results Sector 1 MgF2 SiO2 Sector 2 Sector 3 MgF2 SiO2 Sector 6 102
Experimental Results extracted from the April 2002 data: 600 AMeV
Sector 1
MgF2 SiO2
Sector 2
Sector 3 MgF2 SiO2
Sector 6
102 82
114 97 94
122
150 ??
L. Fabbietti (TU-München)

13. 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.
L. Fabbietti (TU-München)