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The interaction of K--mesons with photographic emulsion nuclei - Part II. The emission of hyperons from K--interactions at rest

par Bhowmik, B.;Evans, David;Falla, D.;Hassan, F.;Kamal, A.A. A.A.;Nagpaul, K.K. K.K.;Prowse, D.J. D.J.;Rene, Monique ;Alexander, G.;Johnston, R.H.W. R.H.W.;O'Ceallaigh, C.;Keefe, D.;Burhop, E. H S;Davis, Dudley;Kumar, Rajendra R.C.;Lasich, W.B. W.B.;Shaukat, M.A.;Stannard, Russell;Bacchella, M.;Bonetti, A;Dilworth, Constance ;Occhialini, Guiseppe ;Scarsi, Livio;Grilli, M.;Guerriero, L.;von Lindern, L.;Merlin, M.;Salandin, A.
Référence Il Nuovo cimento, 14, 2, page (315-364)
Publication Publié, 1959-10

Article révisé par les pairs

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Résumé :

The emission of Σ-hyperons from 3 037 K- capture stars at rest in nuclear emulsion has been studied. The identification of the hyperons is discussed. Charged Σ-hyperons are emitted from (17.6±1.0)% of all K--stars while (9.6±0.6)% of them lead to the emission of both Σ-hyperons and π-mesons. The Σ-/Σ+ ratio for all stars is 0.86±0.12 while for stars in which a π-meson is also emitted it is 0.45±0.10. The difference between this latter value and the markedly different value (2.0) obtained for K--interactions at rest in a hydrogen bubble chamber is attributed to the Fermi motion of nucleons in the nucleus, and a dependence of the relative K- transition amplitudes on the energy of relative motion of the K--meson and nucleon. The branching ratio, R, of the number of Σ+ decays to π+ and proton respectively is 1.23±0.27. The stable prong distribution of the stars in which a hyperon is emitted, as well as the energy distribution of the Σ-hyperons at emission has been studied. About 16% of all identified charged Σ-hyperons had an emission energy above 60 MeV, and had to be attributed to multi-nucleon interactions of the K--meson. It is estimated that the proportion of all multi-nucleon primary capture prccesses may be as high as (30÷40)%. The interaction of a K--meson with a pair of neutrons seems to occur rarely, if at all. From the fraction of Σ+ emitting stars which also emit a π--meson it is concluded that only about 10% of the π--mesons fail to escape from the nucleus in which capture occurs. This could be understood if K--capture occurs predominantly in the peripheral region of the nucleus. From a similar study of Σ- emitting stars it is found however that the proportion of π+ or π0-mesons, or both, that are absorbed in the nucleus is much higher. Estimates are made of the mean free path in nuclear matter of Σ-hyperons and π0-mesons. Most of the one-nucleon interactions leading to Σ-hyperon production take place with protons and the transition amplitudes corresponding to the T=1 state of isotopic spin is smaller than the T=0 transition amplitude. © 1959 Nicola Zanichelli Editore.