Out of 1242 decay events observed in a magnetic cloud chamber array triggered on penetrating showers, a total of 54 associated $V$-particle pairs has been obtained. All the associations observed are consistent with the "strangeness" selection rules. A statistical analysis of the numbers of double and single events has been used to obtain rough estimates of the fractions of neutral $K$ particles and neutral hyperons which decay by "invisible" modes, and of the relative frequencies of occurrence of various production processes. The main uncertainties in the resulting values are discussed in detail.

• Received 4 September 1956

DOI:https://doi.org/10.1103/PhysRev.104.1703