Cosmic-Ray Mesons near Sea Level

The differential and integral intensities of mesons have been studied using delayed coincidence, anticoincidence, and coincidence methods. It is shown that the differential range spectrum of slow mesons is nearly flat out to 100 g ${\mathrm{cm}}^{-2\mathrm{}}$ of air-equivalent at sea level and at Echo Lake (3240 meters). The zenith angle distribution of slow mesons has been measured, and can be expressed by ${cos}^{3.3}\theta$ at Ithaca and ${cos}^{3.1}\theta$ at Echo Lake. Three independent measurements of the differential intensity of mesons lead to a value of (6.0±0.15)×${10}^{-6\mathrm{}}$ ${\mathrm{sterad}}^{-1\mathrm{}}$ ${\mathrm{g}}^{-1\mathrm{}}$ ${\sec .\mathrm{}}^{-1\mathrm{}}$ at a range of 105 g ${\mathrm{cm}}^{-2\mathrm{}}$ of air-equivalent at Ithaca, New York (260 meters). The sea level electron intensity is considered, and it is concluded that this intensity is consistent with the electron-2 neutrino decay scheme for the $\mu$-meson provided there is a source in addition to mesons contributing electrons with a very steep zenith angle distribution.