The Variation of the Ratio of Positive to Negative Cosmic-RayμMesons with Momentum and Altitude

I. The mean lifetime of ${\mu }^{\pm }$ mesons in carbon and sulfur has been measured by the delayed coincidence technique. Data for decay times >2μsec were analyzed by the statistical method of Peierls and yield ${{\tau }_s}^{+}=2.09\mathrm{}\pm 0.05$μsec for the mean life of the ${\mu }^{+}$ meson in sulfur and ${{\tau }_c}^{-}=1.92\mathrm{}\pm 0.04$μsec for the mean lifetime of the ${\mu }^{-}$ meson in carbon. ${{\tau }_s}^{+}$ compares favorably with values found in material of low atomic number, but there appears to be a significant difference between these values and those obtained in high $Z$ materials. Assuming a $Z^4$ dependent capture probability for ${\mu }^{-}$ mesons, ${{\tau }_c}^{-}$ is compatible with other lifetimes determined in materials of higher $Z$.