The Decay of V 0 Particles

In a set of 23,000 cloud-chamber photographs taken in a study of penetrating showers, 134 examples of the decay of neutral $V$-particles, and 18 of the decay of charged $V$-particles, were observed. An analysis of the 152 examples leads to the following principal conclusions: (1) $V$-particles result from the impact of mesons and probably also of nucleons, upon nuclei. (2) $V$-particles are generally produced singly and not in pairs. (3) Two independent kinds of data, one based on measurements of angles and other purely spatial relationships, and the other based on measurements of momentum and specific ionization, lead to the conclusion that more than 80 percent of these neutral $V$-particles decayed by the production of a heavy positive and a light negative particle. The mass of the heavy positive particle in most instances was consistent with that of a proton, but in a few cases may have been somewhat less. The negative particle appeared most often to be a $\ensuremath{\pi}$-meson, although in a few cases a $\ensuremath{\mu}$-meson was indicated. In about 7 percent of the cases, the positive particle was light and had a mass consistent with that of a $\ensuremath{\pi}$- or $\ensuremath{\mu}$-meson. In these cases the mass of the negative particle was not well determined. So far, therefore, in these investigations, there is no direct evidence that a neutral $V$-particle decays into two $\ensuremath{\pi}$-mesons, or into a positive $\ensuremath{\pi}$-meson and a negatively charged proton, although a few cases may be so interpreted. (4) The data are consistent with the assumption of a two-body decay for a majority of the neutral $V$-particles, and therefore a rather extensive analysis is given based upon this assumption. (5) The energy release, or $Q$-value, of the decay of neutral $V$-particles was computed, on the assumption of a two-body decay, for those cases in which the production of a heavy positive particle was clearly indicated, and where momentum measurements were possible. On the assumption of a decay into a proton and a ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson, the $Q$-values obtained ranged from 10 Mev to about 100 Mev. The great majority of cases however, may be described in terms of discrete $Q$-values at 35\ifmmode\pm\else\textpm\fi{}3 Mev, and 75\ifmmode\pm\else\textpm\fi{}5 Mev, although, of course, the data are consistent with distributions about these values. For the same set of cases, if the positive particle is assumed to be as light even as $1250{m}_{e}$, and/or the negative particle is assumed to be a $\ensuremath{\mu}$-meson, the distribution of $Q$-values is not greatly changed, and the apparent necessity for at least two different $Q$-values remains. In those few cases mentioned in (3) above, in which the positive particle was light, and in which the mass of the negative particle was undetermined, the energy release, computed on the basis of a two-body decay, depends upon the assumed identity of the decay products, and is about 100-130 Mev for the assumption that two $\ensuremath{\pi}$-mesons are produced, about 50-80 Mev for a positive $\ensuremath{\pi}$-meson and a negative $\ensuremath{\tau}$-meson, and about 30-80 Mev for a positive $\ensuremath{\pi}$-meson and a negative proton. (6) The rest mean lifetime of ${V}^{0}$ particles, which appear to yield protons and ${\ensuremath{\pi}}^{\ensuremath{-}}$-mesons as decay products, was found to be 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec for 26 cases having $Q$-values greater than 50 Mev, and 2.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec for 48 cases having $Q$-values less than 50 Mev, on the assumption of a two-body decay. In view of the rather poor statistics, the above two lifetimes are consistent with a single value, and lead to an average of 2.5\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. The above lifetimes are not appreciably changed if a multibody decay of the neutral $V$-particle is assumed. (7) The data are not adequate to distinguish conclusively between a two-body and a multi-body decay, and, therefore, a discussion is also given in terms of a variety of possible decay schemes of the neutral $V$-particle.