A1 Collaboration
The Cerenkov Counters

Spec. A Cerenkov Detector

All three spectrometers of the A1 collaboration are equipped with similar detector systems.

The Cerenkov counters are part of the trigger system and are necessary to identify electrons and charged pions. In the momentum range of interest these particles are not distinguishable by the scintillation detectors of the trigger system, since they are both minimum ionizing particles. The Cerenkov counters are designed to give a signal if an electron passes the detector; a charged pion gives no signal. Therefore we can suppress electrons and identify charged pions by using the Cerenkov detector as a veto counter. On the other hand it is sometimes useful to have a good electron identification if there is a lot of background.


Main mirrors:

Winston-funnel mirrors:

Radiator gas:


The efficiency of the detectors is tuned to have at least eight photoelectrons reaching the first dynode of one of the photomultipliers per event. This gives an efficiency of at least 99.966%. We checked the efficiency with a three detector setup, using large scintillator paddles behind the Cerenkov counters. For spectrometer A, C we have an integral efficiency of 99.98%. For spectrometer B this value counts not for the full acceptance, since 2% of the momentum acceptance at the lower end are not "seen" by the Cerenkov detector.

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Last modified: Thursday, 27. October 2005, 14:45