Nuclear interactions of negative K-masons in nuclear-research emulsion

Summary  A large emulsion stack was exposed at the Bevatron to K- mesons of life time of the order of 10-8 s. Fifty-two K- particles were observed, among which 12 stopped with no visible decay or interaction, 28 ended in an evaporation star, 9 gave a fast π-meson as well as an evaporation star, 1 ejected a hyperon and a π--meson, 1 produced the emission of what may be either a hyperdeuteron coming to rest or a ⌆+ decaying into a proton in flight, and there is 1 case of an evaporation star closely associated with a possible ∧0-decay. Particular importance is attached to the possible hyperdeuteron as the existence of such a particle would be in contradiction to the theory of Gell-Mann as well as allowing one to estimate the strength of the nuclear interaction of the hyperon involved. The main features of the nuclear events are (i) the overall average excitation energy of the evaporation stars is about 150 MeV, (ii) π-mesons are emitted from about 17 percent of the events and most of these, if not all, are negatively charged, (iii) charged hyperons are emitted from a small fraction of the events (one in our case, accompanied by a π-meson), (iv) the mean kinetic energy of the emitted π-mesons is 40 MeV, and (v) the mean prong number of the evaporation stars associated with re-meson emission is significantly greater than the overall average. All these features can be explained qualitatively by one mechanism: the K--particle enters into the nucleu sthen interacts with one nucleon in the presence of other nucleons which take up part of the available energy according to the reaction K-+N +nucleons → Y+ π+nucleons+Q. As the primary absorption process occurs fairly near to the nuclear surface, the secondaries from this reaction each have a probability of about 50 percent of escaping without contributing to the nuclear excitation. The hyperons involved appear to be the ∧0 and the isotopic-spin triplet ⌆+, ⌆0, ⌆-; and the observations require that the production of ∧0’s is of the order of ten times more frequent than that of any particle of the ⌆ group.