The decay of negative π-mesons stopped in light elements and insulators

Positive and negative beams of 170 MeV/c π-mesons, from which the π-mesons were selected by time-of-flight, were stopped in Be, B4C, Teflon and Al targets. The ratio of the numbers of electrons produced in the negative and positive beams, by π-Μ-e decay, was determined for each of these materials. Assuming that no decay of negative π-mesons occurs in the Al target, an upper limit of one per cent is found for the decay probability of negative π-mesons stopped in either Be, B4C or Teflon.