1. C. M. Garelli, B. Quassiati andM. Vigone:Nuovo Cimento,17, 786 (1960).
2. No sure example of Ξ−hyperon was found but in 8 cases out of 2945 stars it was not possible to distinguish between Σ− and Ξ−-decays. The value of the cross section for Ξ− production by K− given byAlvarez (2) is 0.02 mb per nucleon: according to this figure the number of Ξ−-hyperons produced in the 2945 interactions studied by us in the emulsion would be of the order of one or two, so that our result is not inconsistent with the very low value of the cross-section for Ξ− production.
3. C. W. Alvarez:Report at the Kiev high Energy Nuclear Physics Conference (1959).
4. C. Dilworth:Report on the Seventh Annual Rochester Conference (1957).
5. Y. Eisemberg, W. Koch, E. Lorhmann, M. Nikolić, M. Schneeberger andH. Winzeler:Nuovo Cimento,9, 745 (1958).