First observation of radiative photons associated with the µ − transfer process from (tµ − )t o 3 He through an intermediate (t 3 He µ − ) mesomolecule

For the first time, we have observed the 6.76 keV radiative transition photons associated with the µ − transfer process from (tµ − ) atoms to 3 He nuclei through intermediate (t 3 He µ − ) mesomolecule formation in a solid T2 target. The radiative decay branching ratio of the (t 3 He µ − ) mesomolecule and the muon transfer rate were determined and compared with theoretical values. We also studied an accumulation process of 3 He atoms in a solid T2 target by observing the neutron decay rates originating from t-t muon-catalyzed fusions. Their time dependence indicates a sudden 3 He bubble formation in the solid T2 at