Decay of Neutral Pions

Abstract

The proper mean life of the neutral pion is measured by a new method which utilizes a large relativistic time dilation. Negative pions of 3.5 Bev were permitted to make interactions in $K-5\mathrm{}$ nuclear emulsion. High-energy neutral pions from some 2000 interaction stars were observed when they decayed by the Dalitz mode. The distances from the star centers at which they decayed were accurately measurable. The momentum spectrum of the neutral pions was assumed to be the same as that of the charged pions produced in the same interactions. Angular distributions of the secondary charged and neutral pions are presented separately. The mean transverse momentum of the charged pions was measured and found to be 250±10 Mev/c. The neutral pion mean life is (${1.9}_{-0.8\mathrm{}}^{+1.3\mathrm{}}$)×${10}^{-16\mathrm{}}$ sec.