A large nuclear emulsion stack was exposed in the magnetically analyzed beam of $K^{+}$ particles, at the Berkeley Bevatron. The secondaries of stopped $K$-mesons have been analyzed, and examples of all the known modes of decay: $K_{\mu 2}$, $K_{\pi 2}$, $K_{e3\mathrm{}}$, $K_{\mu 3}$, $\tau$, and ${\tau }^{\prime }$ have been identified. The decay processes of the $K_{\mu 2}$, $K_{\pi 2}$, and ${\tau }^{\prime }$ mesons have been confirmed, and a possible decay scheme for the $K_{\mu 3}$ has been considered. The masses of the particles decaying in the different ways have been determined from momentum-range measurements, and for $K_{\mu 2}$ and $K_{\pi 2}$ particles, from the $Q$ of the decay as well. The masses of all the particles are consistent with a value of $965m_e$, within about $10m_e$. The relative frequencies of the various modes of decay have been estimated, and by comparison with other data, it is found that the apparent lifetimes of all the particles are ∼1×${10}^{-8\mathrm{}}$ sec.

• Received 21 October 1955

DOI:https://doi.org/10.1103/PhysRev.101.1085