Zenith Angle and Momentum Spectrum ofμ-Mesons at Sea Level

The zenith angle dependence of the $\mu$-meson intensity at sea level has been measured for several values of momentum between 280 and 1080 Mev/c. Results were obtained by three methods: the coincidence, anticoincidence, and delayed coincidence methods, and it has been found that the shape of the zenith spectrum depended on which technique was used. The delayed coincidence method was capable of determining meson intensities in the presence of other types of penetrating particles. It suggests the existence of a considerable number of nonmesonic particles in the low energy region of the hard component. The lifetime of the meson was computed from its anomalous absorption in the atmosphere. It was found to be 2.2±0.3 microseconds.