RICH 2002 L. Fabbietti (TU-München)

Photon Detection Efficiency in the Photon Detection Efficiency in the CsI-based HADES RICHCsI-based HADES RICH

• Description of the HADES RICH

• OEM Measurement • Single Photon Response

• N0 Calculation

• Summary

RICH 2002 L. Fabbietti (TU-München)

The RICH DetectorThe RICH Detector

Photon Detector :• CH4 MWPC• CsI cathode• 28.600 pads• 10 s readout

C + C @1 AGeV

Lepton Rings

Single Photon Response is CRUCIAL

RICH 2002 L. Fabbietti (TU-München)

pad plane

tank

window

mirror

tank shell

target

radiator gas

detector gas

beam

field plane

photon detector

Efficiency CalibrationEfficiency Calibration(Online Efficiency Measurement (OEM))(Online Efficiency Measurement (OEM))

Photons produced by 600 AMeV 12C beam particles passing two

different solid radiators

beam

Calibrated light source !

n() -> C()

1

0.8

0.6

0.4

0.2

0.0 120 140 160 180 200 220

SiO2

MgF2Tra

nsm

issi

on

[nm]

RICH 2002 L. Fabbietti (TU-München)

OEM RadiatorOEM Radiator

2cm

beam

beam line

RICH 2002 L. Fabbietti (TU-München)

single 12C hit

beam pipe shadow

Single Particle ResponseSingle Particle Response

Nph ~ N0 * Z2100 evt accumulated

MgF2

SiO2

RICH 2002 L. Fabbietti (TU-München)

Single Photon

Pattern

Single Photon Response of Single Photon Response of MWPCMWPC

Pad X Coordinate

Pad

Y C

oord

inat

e

Pul

se H

eigh

t

–Photon Candidates : Local Maxima in an isolated 3X3 Pattern

–Single Pads below Threshold (4 and Charge Particle are cleaned

1 Event

Q Mean = 7 * 10 4 e-

SE ~ 90%

wires

6 mm

6 m

m

RICH 2002 L. Fabbietti (TU-München)

Coupling to Neighbouring PadsCoupling to Neighbouring Pads

Along the wire

photon impact resolution ~ 0.5 mm

Perpendicular to wire

RICH 2002 L. Fabbietti (TU-München)

Charge Distribution of Single Charge Distribution of Single PhotonsPhotons

Simulation

Experiment

single photon response

well understood

RICH 2002 L. Fabbietti (TU-München)

OEM Analysis OEM Analysis

Experimental Data Simulation Input (HGeant)(HGeant)

– Optical parameters (all independently measured)

– Simulation of single photon response

– Electronic noise

N0=102100 Events

Beam pipe shadow

C@600 AMeV

RICH 2002 L. Fabbietti (TU-München)

–150 nm

205

nm

205

nm

145

nm

163

nm

Wave Length Resolved Efficiency Wave Length Resolved Efficiency

MgF2

Radiator

Simulation

ExperimentSector 2

SIO2

Radiator

MgF2 SiO2

RICH 2002 L. Fabbietti (TU-München)

NN00 Calculation Calculation

4 .

( ) ( ) ( ) ( )

R ( ) ( )

i Gas CsI Windowi

Mirror CH Se

T QE T

T

2

04 10

1

2. ( ) ( ) ( )Exp SimC F i

i

dN const T R

Translation to HADES C4F10 Radiator

RICH 2002 L. Fabbietti (TU-München)

NN0 0 ResultsResults

Sector 1

MgF2 SiO2

Sector 2

MgF2 SiO2

Sector 3 MgF2 SiO2

Sector 6

MgF2 SiO2

102 102 102 102 102 102 102 102

82 114 97 102 94 122 102150

??

Experimental Results extracted from the April 2002 data: C @ 600 AMeV

RICH 2002 L. Fabbietti (TU-München)

• 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.

Conclusions and OutlookConclusions and Outlook

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