Heavy Meson Lifetimes

Abstract

Two identical nuclear emulsion stacks were exposed at different distances to the 114-Mev Bevatron $K^{+}$-beam using the same geometry and Bevatron conditions. A comparison of the $K_L$ to $\tau$-meson ratios in the two stacks combined with the known lifetimes of the $K_{\pi 2}$ and $K_{\mu 2}$ gives ${(1.18\mathrm{}}_{-0.28\mathrm{}}^{+0.55\mathrm{}}$)×${10}^{-8\mathrm{}}$ sec for the ${\tau }^{+}$ lifetime. The ratio of the ${K_{\pi 2}}^{+}$ to the ${\tau }^{+}$ lifetime is then 1.03 with a root-mean-square error of ±29%. Thus the $\tau$ and the $K_{\pi 2}$, which according to Dalitz-type analysis should be different particles, have the same lifetime within experimental errors. The $\tau$ and $K_L$ lifetimes can be obtained by a second method which does not rely on any previous lifetime information. In this method the ratios of the heavy meson fluxes to the proton and pion beam fluxes are compared. The results obtained by this method are ${(1.04\mathrm{}}_{-0.23\mathrm{}}^{+0.42\mathrm{}}$)×${10}^{-8\mathrm{}}$ sec for the ${\tau }^{+}$ lifetime and ${(1.11\mathrm{}}_{-0.11\mathrm{}}^{+0.18\mathrm{}}$)×${10}^{-8\mathrm{}}$ sec for the ${K_L}^{+}$ lifetime. Alternate $\tau$ and $K_{\mu 3}$ fluxes in the two stacks also indicate a lifetime of about ${10}^{-8\mathrm{}}$ sec.