In 1949, members of the University of Rochester Cosmic Ray Group reported the first clear‐cut evidence for the existence of a previously unrecorded nuclear particle, the neutral meson, in the cosmic radiation. From measurements of tracks left in photographic emulsions it was established that large numbers of neutral mesons were produced as a result of the high energy collision between a helium nucleus contained in the primary cosmic radiation and a silver nucleus in a photographic plate. Recent findings of the Rochester group were reported in a paper presented before the American Physical Society meeting in Houston. Texas, on November 30th by Morton F. Kaplon and David M. Ritson, who announced that the lifetime of the neutral meson has been established as being about 10−15 second, the briefest existence yet determined for any elementary particle.

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