Formulation mathématique du modèle de gell-mann

In this paper we present some results on charged heavy mesons. They were obtained with an experimental arrangement consisting essentially of two large cloud-chambers placed one above the other. The top chamber had a magnetic field while the bottom chamber was of the multiplate type. The contents of the different sections of the paper can be summarized as follows: 1. The double cloud-chamber method is compared with other more conventional methods. 2. The apparatus is briefly described. 3. The behaviour in the multiplate chamber of the charged secondaries of V±-decays occurring in the top chamber is disscussed. π-mesons have been identified through their nuclear interactions. The presence of μ-mesons is also strongly suggested by:a) the long mean free path of the secondaries andb) one direct mass measurement. 4. S and slow V±-events observed in the multiplate chamber are discussed. It is shown that one should distinguish between two groups of decays: One with secondaries of range smaller than 20 g cm−2 of Pb, the other with larger range secondaries. Although the first group can be due to τ-mesons, the second group cannot be so explained, at least not phenomenologically. 5. The results of mass measurements—from range and momentum—on the primaries of the second group of events are presented. The measurements agree with a unique value of (914±20) me; which appears to be different from the τ-mass. 6. We show that some, and probably most, of the secondaries of this second group of events are μ-mesons. This conclusion is based on the dynamics of the decay and results from the measured mass of the primary particle and the observed ranges of the secondaries. The observation of one large angle scattering indicates, however, that τ-mesons may also be present among the secondaries.

Étude des mésons K chargés, au moyen de deux chambres de Wilson superposées

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

A total of 3,480 K/sup -/-mesons were observed. Of these, 445 interact in flight, at a mean energy of 40 Mev and only their general characteristics were studied. Little difference was observed between the number of unstable charged particles ( SIGMA plus or minus -hyperons and pi plus or minus -mesons) in these interactions and those in the 3,035 interactions at rest. The 3,035 K/sup - /-interactions at rest were studied in detail. The results on those interactions in which pi -mesons are emitted are given. An estimate of the SIGMA -hyperon nuclear potential is based on the energy spectrum of pi -mesons emitted in the K/ sup -/-interactions in which the only charged particles emitted are a pi meson and a SIGMA -hyperon. A detailed examination of ihe angular distribution of 2- pronged events, and of the sign ratio of the pi -mesons, the prong distribution and energy release in all events led to an estimate of the probabilities of absorption of positive and negative SIGMA hyperons in the parent nucleus, and to a partition of the events between the various primary reactions. (auth)

The interaction and decay of K- mesons in photographic emulsion - Part I. General characteristics of K--Interactions and analysis of events in which a charged π-meson is emitted

A large emulsion stack, exposed at high altitude, has been used to study the decaymodes of K-particles which produce a single charged secondary. The 5 decay modes, K
 μ
 , χ, ϰ and τ′ have been recognized from the nature and energy of the charged secondary. The masses of the parent particles of the two-body decay modes, K
 μ
 and χ found from the mean range of the charged secondary are (976±7) me and (969±3) me respectively. Independent values derived from measurements of the scattering of the secondary track near the decay point are (954±17) me and (972±15) me respectively. The reliability of these mass values is discussed. An examination of the relative frequency of the decay modes in these experimental conditions indicates that the K
 μ
 -and χ-modes constitute respectively about 67 % and 20 % of all the K-particle decays: the Kβ, ϰ- and τ′-modes being present to about 9 %, 3 %, and 1 % respectively.

On the masses and modes of decay of heavy mesons produced by cosmic radiation

After a description of the methods used in the measurements of momentum and range, the data on 46 S-events obtained with a double cloud-chamber experiment are examined. Momentum-range measurements on 22 positive S’s give a mass consistent with a single value at (928 ± 13) me. The analysis of the ranges of the secondaries shows, however, that not all S-events can be explained by a single decay mode. A large proportion of the secondaries correspond to a light meson of unique range (75.7 ± 1.7) g·cm−2 Cu. The comparison of this range with the measured masses of the primary particles proves that these secondaries are μ-mesons. The accompanying neutral secondary is shown at the same time to be a particle of zero mass. The absence of cascade showers associated with S-events with long-range secondaries shows that the neutral secondary is a neutrino. The decay mode Kμ → μ + ν previously proposed is more firmly established. Two independent mass estimates are obtained for the Kμ-particle. One—from momentum-range measurements—gives directly (906 ± 27) me. Another—from the mode of decay and the range of the μ-secondary—gives indirectly (941 ± 11) me. A final best mass of (935 ± 15) me is obtained by the combination of the two estimates after taking into account possible additional errors. The Kμ-particle is then shown to be essentially positive and to constitute (66 ± 18)% of the S’s which passed through the top chamber. No precise information can be obtained as to the mode of decay of S-particles which are known not to belong to the Kμ-decay mode.

Further discussion of the K μ decay modedecay mode

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

Study of charged k mesons by means of two superposed wilson chambers

Sur le signe de la particule Kμ

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