The Instability of the Meson

Values of the proper lifetime of the meson have been deduced from a comparison of the intensity of mesons in an inclined direction under air with that in the vertical under a superposed lead shield equivalent in absorbing power to the difference between the masses of air traversed by the mesons before reaching the apparatus in the two directions. The required mass of lead was calculated from the Bethe and Bloch formula. The reliability of this use of the formula has been verified by an experimental determination of the relative stopping powers of water and lead. We calculate from our experimental data that the average proper lifetime of all mesons having energies exceeding 6.1×${10}^8$ ev upon reaching the apparatus is equal to 3.9±0.3 microseconds, and the average proper lifetime of all mesons with energies exceeding 11.9×${10}^8$ ev upon reaching the apparatus is equal to 3.8±0.4 microseconds. From the same data, the proper lifetime of only those mesons having about 9×${10}^8$ ev energy upon reaching the apparatus is equal to 2.6±0.8 microseconds. With the theory of Euler and Heisenberg, the proper lifetime has also been calculated from measurements of the number of disintegration electrons and their secondaries in equilibrium with the mesons in air. The value obtained by this method is roughly equal to 6 microseconds.