V-Particle Production by 1.9-Bevπ−Mesons

A twenty-atmosphere hydrogen-filled diffusion cloud chamber located in a magnetic field of 10 500 gauss was exposed to a beam of 1.9-Bev ${\pi }^{-}$ mesons from the Brookhaven Cosmotron. Out of 20 000 pictures taken of the chamber there are two examples of $V$-particle production in the gas of the chamber, and 78 examples of decays of $V$ particles which were presumably produced in the stainless steel walls of the chamber. One of the production events in the gas of the chamber is best interpreted as ${\pi }^{-}+p\to {\Lambda }^0+K^0+{\pi }^0$, while the other is an example of ${\pi }^{-}+p\to {\Sigma }^{-}+K^{+}$. The 63 neutral decays observed include 28 identified ${\Lambda }^0$ particles and 11 identified ${\theta }^0$ particles. Momentum and angular distributions for the ${\Lambda }^0$ and ${\theta }^0$ particles were obtained. Six of the $V^0$ decays, or about 10%, were classified as anomalous. Of these, three seemed to represent the $\beta$ decay of neutral $V$ particles into ${\pi }^{\pm }+e^{\mp }+\nu$. From the data on neutral $V$-particle decays the mean lifetime of the ${{\theta }_2}^0$ was qualitatively measured as being probably between ${10}^{-9\mathrm{}}$ and ${10}^{-8\mathrm{}}$ sec. The cross section for $V$-particle production by 1.9-Bev ${\pi }^{-}$ mesons on protons is estimated to be ∼1 mb. Some evidence was found which suggests the existence of a heavy cascade $K$ meson which decays into a conventional $K$ meson and a pion.