1.5.1 Depommier et al. (1968)
The earliest precise measurement of the p + -> p 0
e+ n branching ratio was performed by Depommier et
al. and reported in 1968 [Dep 68]. This measurement was done at the CERN
synchrocyclotron using stopped pions. Pion beta decay events were identified by
the g g coincidence from a p 0 decay in an array of
lead glass detectors (see Figure 1.4). The data acquisition system consisted of
two oscilloscopes with cameras triggered by this coincidence. Punch tape was
also used for storing some digitized
Figure 1.4: The experimental setup from [Dep 68]. Both front and side views
of the leadglass calorimeter are shown. Pions pass through the carbon block
which slows them so that they stop in counter 3. The pions decay and the
leadglass calorimeter detects the back-to-back 2 g signature
of a p 0 decay.
information. The experiment yielded a value (1.00
)×10-8
for the pion beta decay branching ratio.