Hugh Muirhead coauthored the 1947 observations that distinguished charged pions from their lighter decay products. In a nuclear emulsion, one stopping particle track was followed by another emerging from its endpoint. Track ranges and ionization provided evidence for a two-stage process involving different masses. The recorded geometry made a decay recognizable even though neither particle was directly followed in real time.[ref]
Processes Involving Charged Mesons by Cesare Mansueto Giulio Lattes and others. 1947, connected meson tracks and interpretation of the stopping-particle events
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