We have found a long-lived metastable state of stopped - in liquid helium by measuring the time spectra of two different delayed products: (i) protons emitted after - absorption by He4 nuclei and (ii) 70-MeV electrons originating from free -'e-e» decay. The lifetime and fraction of delayed - absorption obtained by using the emitted protons are 7.26"0.12 nsec and 1.66"0.05%, respectively. The free-decay fraction of a pion in liquid helium was obtained to be 0.64"0.03% from this result, which is consistent with the observed free-- decay fraction. These results imply that 2.30"0.07% of stopped - are trapped in the metastable state which have an overall lifetime of 10.1"0.2 nsec. The same experimental and analysis were performed for stopped - in liquid neon, where no evidence for trapping was found.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics