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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