Cloud Chamber Investigation of Anomalousθ0Particles

Abstract

Eighteen anomalous ${\theta }^0$, (${{\theta }^0}_{\mathrm{anom}}$), decay events observed in the California Institute of Technology magnet cloud chambers have been analyzed. Many of these decays are dynamically inconsistent with the ${\tau }^0\to {\pi }^{+}+{\pi }^{-}+{\pi }^0$ scheme, but most are consistent with the decay processes: ${{\theta }^0}_{\mathrm{anom}}\to {\pi }^{+}+{\pi }^{-}+\gamma , {\pi }^{\pm }+{\mu }^{\mp }+\nu , \mathrm{and} {\pi }^{\pm }+e^{\mp }+\nu$. However, at least one event is inconsistent with each decay scheme. From the locations of the decays in the cloud chamber, the lifetime is found to be significantly longer than that of the normal ${\theta }^0$ particle, called here the ${{\theta }^0}_{\pi 2}$ particle. Other differences in the behavior of the ${{\theta }^0}_{\mathrm{anom}}$ and ${{\theta }^0}_{\pi 2}$ particles were also observed in the (a) momentum distributions, (b) origin locations, (c) relative numbers of ${{\theta }^0}_{\mathrm{anom}}$ and ${{\theta }^0}_{\pi 2}$ particles traveling upward, and (d) the types of $V$ particles produced in association with the ${{\theta }^0}_{\mathrm{anom}}$ and ${{\theta }^0}_{\pi 2}$. It is concluded that not all the ${{\theta }^0}_{\mathrm{anom}}$ decays can result from alternate decay modes of the ${{\theta }^0}_{\pi 2}$. Moreover, many decays can be neither ${\tau }^0$ decays nor alternate decays of the ${{\theta }^0}_{\pi 2}$.