This article surveys our empirical knowledge of the production processes, the nuclear interactions and the decay processes of K particles and hyperons, as this appeared at the close of 1956, and interprets these phenomena within the framework of the charge-independent classification scheme proposed by Gell-Mann and by Nishijima for these `strange particles'. The assignment of a `strangeness' quantum number to each strongly interacting particle is a deep-lying aspect of this scheme, and the main qualitative features of the empirical data allow a direct interpretation in terms of a law of conservation of strangeness through all strong interactions. Where appropriate, more detailed analyses of the phenomena are made on the assumption that charge independence holds for these strong interactions. The evidence on decay processes for K particles and hyperons is discussed in some detail. These processes violate the strangeness conservation law and also involve changes in the total isotopic spin for those cases where this quantity is relevant for the final particles. The success of Gell-Mann's ?T = ? rule in accounting for certain aspects of the decay data is considered for each of the latter cases; this rule is given a simple origin in Schwinger's model for strange particle decay processes, which is discussed briefly. The implications of symmetry between particle and antiparticle, as pointed out by Gell-Mann and Pais for the neutral K particles and their decay modes, is also discussed in some detail, together with an account of the experimental data on long-lived K? particles and anomalous K? decay modes. Indications in the data which bear on the spin and parity values for K particles and hyperons are stressed, especially for the decay modes associated with ? and ? particles. Although it is shown that the products of ? and ? decay necessarily differ in spin or in parity, a great similarity has been found concerning all other properties of the ? and ? particles, and the proposals which have been made to account for this situation are surveyed. For the ?? particle, observations on bound ?? hypernuclei provide much information relevant to the ??-nucleon interaction and the ?? spin and parity, and this is also discussed in some detail. A section is devoted to discussion of `anomalous events' for which no interpretation is known in terms of the interactions of the well-established particles. These events and the possibility that heavier unstable particles or perhaps resonance states may exist have an obvious importance, of special relevance for attempts to construct a theoretical foundation leading naturally to the Gell-Mann-Nishijima scheme. A brief discussion of the preliminary attempts to establish such a foundation is given. An appendix has been added in proof to discuss the recent observations on the failure of parity conservation and of charge conjugation invariance in certain weak decay processes, and the effects which a failure of these symmetry properties also for strange particle decays would have on the arguments made and the conclusions reached in this survey.

K Mesons and Hyperons their strong and weak interactions

Summary An event which is interpreted as a nuclear interaction of a charged hyperon has been observed in a photographic emulsion. The appearance of the interaction is that of a typical σ-star, but is caused by a particle of protonic mass. Estimates of mass by two independent techniques are in agreement with each other, and are consistent with those of charged hyperons reported by other workers.

LII. Evidence for nuclear interaction of a charged hyperon arrested in photographic emulsion

In a stack of stripped emulsions an example of associated production of a positively charged τ-meson and of a hyperon decaying in flight into a charged L-meson was observed. The mass of the hyperon is found to be 2374−37+29 me, assuming the decay scheme Y±→π±+n+Q. For the τ-meson one obtains from range measurementsmτ=963±0.5 me, all three secondaries coming to rest in the emulsion. A possible reason is suggested why some authors might have slightly overestimated the mass of their τ-mesons.

Associated production of a τ-meson and a charged hyperon

MASS OF THE $Sigma$$sup +$ HYPERON

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

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

Further evidence is presented in favour of the existence of charged unstable particles of hyperprotonic mass. In two cases the decay product is a fast light particle, in one case it is a slow proton. The decay schemes : Ωπ± → n + π+ - +Q; ΩP → p + π0 +Q are proposed for the two types of events respectively. They are possibly alternative modes of decay of the same type of H-particle. The evidence available from photographic emulsion and cloud chamber experiments is discussed.

On the existence of unstable charged particles of hyperprotonic mass

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On the existence of unstable charged particles of hyperprotonic mass