Cloud-Chamber Observations of the Heavy Charged Unstable Particles in Cosmic Rays

Abstract

In a series of pictures taken with a multiplate cloud chamber, we have observed a number of charged unstable particles considerably heavier than 7r-mesons, of which some decay at rest (S particles) and some decay in flight (V ± particles). In each case the charged decay product is a particle of mesonic mass. From our results, which are not yet completely conclusive, it appears that most of the observed events can be explained by the two-body decay of a single kind of particle. The evidence concerning the mass of this particle, its mean life, and the nature of the neutral decay product is discussed. Our observations are compared with those of other experimenters.

The new unstable cosmic-ray particles

“…Thus have photographed a decay in which both secondary particles penetrated several lead plates and then each produced a small nuclear interaction : this unusual photograph is reproduced in Plate VI and shows conclusively that both the secondaries are nuclear interacting particles. Bridge et al (1953 a) have reported a value of (163 i 40) gcm-2 of lead for the interaction length for the secondaries of Vo-particles. Clearly the secondaries could be protons or n-mesons, but the accuracy of this measurement is such that it is impossible to exclude a small fraction of p-mesons or other non-interacting particles.…”

“…Recently Bridge et al (1953 a) have made a number of Q-value measurements on low-energy VIo-particles using data obtained in their multiplate chamber. and d2 (see fig.…”

“…Because of the relatively short lengths of emulsion available in relation to the lifetime of the Vzo, which is approximately 2 x 10-10sec, this evidence cannot be taken to disprove the scheme (111.5). Bridge et al (1953 b) have also searched their S-particle photographs for V,O-tracks or other evidence of the decay of the neutral . .…”

“…The term charged V-particle is applied to those particles, other than p-and 7-mesons, which decay in flight in the cloud chamber to give a typical wide-angle forked track (Plate XIII). Since the initial discovery by the authors (Rochester and Butler 1947), these particles have been found in small numbers by Serif€ et al (1950), Armenteros et al (1951Armenteros et al ( , 1952, Bridge and Annis (1951), Fretter (1951), , Leighton et al (1951), Astbury et al (1952Astbury et al ( a, b, 1953 and Bridge et al (1953 b). It is generally agreed that charged V-particles are rarer than neutral V-particles, and that with the type of counter selection normally used (see 11, $2) the ratio is about 1 : 6.…”