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

Long-lived neutral K mesons

117 interactions of cosmic ray particles with aluminium nuclei have been studied. 101 showers containing no apparent unstable particles yielded the following multiplicities:

$$\left\langle {n_s } \right\rangle = 7.3; \left\langle {n_s^ + } \right\rangle = 3.9; \left\langle {n_s^ - } \right\rangle = 2.7; \left\langle {n_s^ \pm } \right\rangle = 0.6.$$

. The momentum and angular distributions of the secondary particles were examined, and an attempt was made to study the momentum-angle correlation. The mean transverse momentum was 0.31 GeV/c, the RMS deviation about this mean being 0.23 GeV/c. A quantity related to the (U−pL) of the recoil nucleon was also investigated. 12 showers containing one V0 each and 1 shower containing two V0 particles were studied; this showed that the 117 showers contained; 29.5−11.0+14.0 Λ0 and 18.0−10.0+15.0 ϑ0 particles. 3 showers containing V± particles were also studied; one of them was probably a Ξ− particle.

/pdf/an-experiment-on-nuclear-interactions-of-high-energy-10-100-3tf7x4v8ll.pdf

An experiment on nuclear interactions of high energy ((10÷100) GeV)

Using the chsrge exchange of K- in a hydrogen bubble chamber, it was found that K/sup 0/ is 3.7 plus or minus 0.7 Mev heavier than K-. The incident K- ranged in energy from 10 to 150 Mev. A total of 41 charge-exchange events was observed. (W. D. M.)

K ¯ 0 − K − Mass Excess

Elementary particle physics began in the 1930s as an outgrowth of experimental studies of nuclear and cosmic ray physics. It started to develop rapidly after the discoveries of the pion and the strange particles in 1947. Its beginnings and development have already been documented in a number of books [1–4]. The discovery of hypernuclei has also been described by one of its authors [5]. The present article contains previously unpublished material pertaining to this discovery, and also statistical data on the first decade of hypernuclear physics. The early efforts to understand the nature and properties of new unstable particles set a stage (see Fig. 1) on which hypernuclei appeared and provided an important piece to solve the jigsaw puzzle.

Hypernuclei (and strange particles) — how it all began? ∗

A study of 161 V0-decays observed in the momentum chamber of the Ecole Polytechnique at the Pic du Midi has been made. These events correspond to a strict choice based on the measurability of the momenta of both secondairies (better than 10%). The main results are: 1) No direct evidence for anomalous neutral hyperon decays. Upper limits (6 to 8%) can be placed on the existence of various hypothetical modes. 2) TheQ-values for the λ0-decay:$Q_{\Lambda ^0 } = (37.9 \pm 0.4)$ MeV. 3) The direct identification of the π nature of both secondaries of the θ0-decaymode. 4) TheQ-value for θ0-decay:$Q_{\theta ^0 } = (217 \pm 4)$ MeV. 5) A direct proof of the non identity of the particles responsible for the θ0-decay and the anomalous V0-decays based on the signincant difference between the number of slow and fast events of each category.

On theQ-values of the λ0 and the θ0 and on the anomalous V0-decays

Description and discussion of an anomalous V0-decay of particular interest discovered in a survey of photographs taken in the Ecole Polytechnique magnet cloud chamber.

A V0-decay with an electron secondary

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On theQ-values of the λ0 and the θ0 and on the anomalous V0-decays

A V0-decay with an electron secondary