Properties of negative K-mesons

Abstract

An analysis of interactions of 420 MeV/c K−-mesons incident on a nuclear emulsion stack has been carried out. By following K−-mesons along the track, we obtained information on the interaction of K−-mesons in flight and at rest. The differential scattering cross-section was fitted with diffraction scattering off a black disk with radius 1.32 ·A1/3 fermis in agreement with the total reaction cross-section. A compilation of K−-H elastic scattering and absorption events is presented, giving cross-sections of Σkh (scattering)= (48.4−11+15) mb and (ΣKH (absorption) = (11.4-5+9) mb. The inelastic scattering of K−-mesons in complex nuclei has been found to be only 4% of the absorption cross-section. The average energy losses in K− inelastic scattering events is ~ 50% of the incident K energy, in contrast to a 25% loss for K+ inelastic scattering. In the course of this work we have observed a number of decays in flight. Combining these with earlier data, we obtain a mean life of τκ-=(1.3+0.4-0.3)·10-8s. We have identified some of the secondaries from decays in flight, namely 2 Kπ2, Kμ2, and 1Ke3. From K−-H absorption events we have obtained a Σ−Σ+ mass difference of (13.9±1.8) me and a value of the K- mass of (966.7±2.0) me. From an analysis of the charged pion spectrum obtained from K- interactions at rest, it was possible to calculate the ratio of λ to Σ hyperons produced in the primary interaction. We find that in the primary K− nucleon absorption reaction, Σ-hyperon formation dominates over λ-hyperon formation. An energy and strangeness balance shows that 70% of the K− stars at rest emit a λ-particle. This means that about 60% of the Σ-hyperons that are produced are converted to λ-hyperons inside the nucleus in which they were formed.