MASS OF THE POSITIVE PION.

Abstract An improved value of the mass of the positive pion is reported, the result being m π + = 139.584 ± 0.25 MeV/ c 2 . When compared with the mass of the negative pion this result may be regard as a verification of the calculations relating π − to the measured 4f - 3d transition energies in pionic calcium and the titanium. Alternatively, the ratio of the two masses may be regarded as a check of CPT invariance.