Properties of Heavy Unstable Particles

A block of emulsion consisting of unbacked emulsion sheets can be used as a very efficient detector for heavy unstable particles and provide favorable conditions for mass and energy determinations. The mass of the $\tau$ meson was obtained as $m_{\tau }=3\mathrm{}{m}_{\pi }+Q$, where $Q=76.0\mathrm{}\pm 0.9$ Mev. Fairly accurate mass values are obtained for the positive $K$ meson and four examples of the capture of negative heavy mesons are presented, two of them leading to emission of a $\pi$ meson. A charged particle of mass higher than that of a proton which decays in flight into a meson is discussed. In most of these cases the nuclear event giving rise to the heavy mesons could be observed. The $Q$ value of the ${V_1}^0$ particle was determined as 37±2 Mev and other examples which may represent the decay of neutral particles are discussed.