XLIV. Cloud chamber observations of negative heavy mesons

Earlier work by the Manchester Jungfraujoch group on slow, negative, heavy cosmic-ray particles observed in a magnet cloud chamber has been repeated. An upper limit to the frequency of slow K−-mesons which do not decay in the cloud chamber is now found to be ∼1% of the frequency of slow protons. From other published data the probable ratio of the two frequencies is estimated as about 1 : 2000. The identity of the observed particles is discussed. The previous results giving a high frequency and a long mean lifetime for K−-mesons are not confirmed. One event showing the possible simultaneous production of two slow K−-mesons and one example of an upward-moving S+-particle are described.