Initial Tests Of The Pion Beta Decay Detector

1.4.1 Czapek, et al. (1993)

In 1993, results were reported for a measurement of the p -> e n ( g ) branching ratio from data taken at PSI in 1988. The experimental setup (shown in Fig. 1.1) consisted of 132 hexagonal BGO crystals which covered all but 0.2% of 4 p . A target made of plastic scintillator was used for stopping the pions at the center of the array.

Figure 1.1: Experimental setup from [Cza 93]. PM indicates the photomultipliers, BGO indicates the BGO calorimeter S indicates a beam-defining scintillator, and T indicates the active target.

BGO crystals on either side of the target were coupled to the target and served simultaneously as light guides to the target and active members of the calorimeter.

Data were taken using two different triggers simultaneously. One triggered on the rare p -> e n ( g ) decays while the other was a prescaled trigger for measuring the normalization events. The branching ratio was found by cutting on a window in the total energy spectrum (83.5 MeV to 101 MeV pion stopping+decays). The low energy tail was estimated using a GEANT simulation. The value obtained was ([Cza 93].