Decay of a ז-meson

A ז-meson decay has been observed in an Ilford G 5 emulsion exposed under 14⋅5 cm of iron at an average height of 35000 ft. Measurements made on the secondary particles suggest that they are all π -mesons. The Q -value of the decay is (79±3⋅5) MeV, corresponding to a mass for the ז-meson of (983±10) m e . The data now available on ז-mesons are briefly discussed.