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The interaction and decay of K--mesons in photographic emulsion - Part III

par Evans, David;Hassan, F.;Nagpaul, K.K. K.K.;Prowse, D.J. D.J.;Rene, Monique ;Alenander, G.;Johnston, R.H.W. R.H.W.;Keefe, D.;Davis, Dudley;Lasich, W.B. W.B.;Shaukat, M.A.;Stannard, Russell;Bonetti, A;Dilworth, Constance ;Merlin, M.;Salanuin, A.
Référence Il Nuovo cimento, 15, 6, page (873-898)
Publication Publié, 1960-03

Article révisé par les pairs

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Résumé :

This paper presents Part III of the series on the interaction of K--mesons in photographic emulsions contributed by the European K-collaboration. The mean free path for K--interaction in flight (10÷80) MeV with hydrogen and with the complex nuclei in emulsion are compared with other recent experimental data. A number of Σ-hyperons are also investigated. From favourable examples of Σ+-p decay recorded in the emulsion the Σ+ mass is estimated as MΣ=2327.2±1.0 mc and from the hydrogen capture (K-+H) events the mass difference (MΣ--MΣ+) is found to be 14.6±1.1 me. Lifetime estimates are also given for the charged Σ hypersons:a) The best estimate for the Σ+ lifetime is obtained using only events in which the decay proton is emitted forward in the centre-of-mass system. Thus τ+=0.82-0.20+0.34·10-10 s. b) A representative value for the hypothetical Σ- lifetime as determined from 70 selected Σπ± decays is 0.71-0.12+0.19·10-10 s. The effective lifetime appears (as well as can be ascertained) to remain of the order of the Σ;+ lifetime, even in samples containing widely different proportions of Σ- hyperons. Although values are greater than the lifetimes previously reported in emulsion esperiments, it still appears possible that a genuine anomaly may exist. The observed numbers of secondary interactions by charged particles emitted from the K--capture stars may be accounted for on the basis of proton interactions, although some contribution from deuterons is not excluded. One definite example of a fast Σ interaction (visible energy release 129 MeV) has been found in a length of 70 cm of track registered in the emulsion. The number of single scatterings in 18 cm of Σ- and 25 cm of Σ+ hyperon track in emulsion (energy interval (5÷100) MeV) are compared with that expected for Coulomb scattering by a point nucleus. Only a slight possible indication of the nuclear interaction of the Σ--hyperon is demonstrated with the few data at present available. In K--interactions giving (Σ+π) some 45 Σp+ and 47 Σπ+ decays were also examined for possible polarization of the decay with respect to the (Σ, π) plane of production. © 1960 Società Italiana di Fisica.