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 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 Σ hyperon and a pion, of such momenta as to make it obvious that K^- capture proceeded according to: K^-+N→Y+π. 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=Λ⁰. One K^- capture reaction (and possibly a few more) was: K^-+2N→Y+N. In this one capture, the hyperon is either Σ^± decaying by an unusual mode, possibly into an electron, or else is a hitherto unknown particle.