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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)
RICH 2002
The RICH Detector
C + C @1 AGeV
Photon Detector :
• CH4 MWPC
• CsI cathode
• 28.600 pads
• 10 ms readout
L. Fabbietti (TU-München)
Lepton Rings
Single Photon Response
is CRUCIAL
RICH 2002
Efficiency Calibration
(Online Efficiency Measurement (OEM))
tank
Calibrated light source !
detector gas
window
mirror
pad plane
tank shell
field plane
Photons produced by 600 AMeV
12C beam particles passing two
different solid radiators
photon detector
beam
target
radiator gas
beam
Transmission
n(l) -> QC(l)
1
0.8
SiO2
0.6
MgF2
0.4
0.2
0.0 120 140 160 180 200 220
l [nm]
L. Fabbietti (TU-München)
RICH 2002
OEM Radiator
beam
beam line
2cm
L. Fabbietti (TU-München)
RICH 2002
Single Particle Response
Nph ~ N0 * Z2
100 evt accumulated
single 12C hit
SiO2
MgF2
beam pipe shadow
L. Fabbietti (TU-München)
RICH 2002
Single
Photon
Pattern
wires
6 mm
1 Event
Pulse Height
Pad Y Coordinate
Single Photon Response of
MWPC
6 mm
Pad X Coordinate
–Photon Candidates : Local
Maxima in an isolated 3X3
Pattern
Q Mean = 7 * 10 4 eeSE ~ 90%
–Single Pads below Threshold
(4 s) and Charge Particle are
cleaned
L. Fabbietti (TU-München)
RICH 2002
Coupling to Neighbouring Pads
Along the wire
 photon impact
resolution ~ 0.5 mm
Perpendicular to wire
L. Fabbietti (TU-München)
RICH 2002
Charge Distribution of Single
Photons
Simulation
Experiment
single photon response
well understood
L. Fabbietti (TU-München)
RICH 2002
OEM Analysis
Experimental Data
Simulation Input (HGeant)
C@600 AMeV
N0=102
100 Events
Beam pipe
shadow
– Optical parameters (all independently
measured)
– Simulation of single photon response
– Electronic noise
L. Fabbietti (TU-München)
RICH 2002
Wave Length Resolved Efficiency
Sector 2
MgF2
Radiator
163 nm
145 nm
205 nm
205 nm
Simulation
Experiment
–150 nm
SIO2
Radiator
MgF2
SiO2
Q
L. Fabbietti (TU-München)
l
RICH 2002
N0 Calculation
 e (l )
i
 TGas (l )  QECsI (l )  TWindow (l ) 
i
R Mirror (l )  TCH 4 (l )  e Se.
Translation to HADES C4F10 Radiator
l2
Exp
N0
 const.  TC4 F10 (l )   e
l1
L. Fabbietti (TU-München)
i
Sim
i
(l )  R (l ) 
dl
l2
RICH 2002
N0 Results
Experimental Results extracted from the April 2002 data:
C @ 600 AMeV
Sector 1
Sector 2
Sector 6
Sector 3
MgF2 SiO2 MgF2 SiO2 MgF2 SiO2 MgF2 SiO2
102
82
L. Fabbietti (TU-München)
102
114
102
97
102
102
102
94
102
122
102
102
102
150
??
RICH 2002
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)
RICH 2002