Interactions of NegativeKMesons

A detailed analysis of events in nuclear emulsions caused by $K^{-}$ mesons is given. Of 39 $K^{-}$ mesons observed, 8 produced stars in flight, 1 underwent nuclear scattering, and 30 were captured at rest. The $K^{-}$ mean free path for inelastic collisions in emulsion is 17±5 cm, at most geometric. Charged hyperons and hyperfragments were seen in 12 stars; in all others, emission of a neutral hyperon is allowed by energy balance. In $\frac{2}{5}$ of the stars, a charged pion was emitted; half of the pions had kinetic energy ⩾ 100 Mev. 3 stars consisted only of a $\Sigma$ hyperon and a pion, of such momenta as to make it obvious that $K^{-}$ capture proceeded according to: $K^{-}+N\to Y+\pi$. Kinematic analysis shows that this reaction was the most likely process in almost all of the other captures. In 5 of the captures at rest, the pion energies were ⩾ 100 Mev, compatible only with $Y={\Lambda }^0$. One $K^{-}$ capture reaction (and possibly a few more) was: $K^{-}+2N\to Y+N$. In this one capture, the hyperon is either ${\Sigma }^{\pm }$ decaying by an unusual mode, possibly into an electron, or else is a hitherto unknown particle.