Measurement of the directional cosmic-ray muon range spectrum

Abstract

The French-U.S. muon experiment, operating in the Mt. Blanc Tunnel between France and Italy for six years, has yielded an extremely precise measurement of the depth-zenith-angle distribution of high-energy cosmic-ray muons. Data were obtained over the depth range of 700 to 5000 hg/${\mathrm{cm}}^{2}$ for zenith angles of 0\ifmmode^\circ\else\textdegree\fi{} to 80\ifmmode^\circ\else\textdegree\fi{} (except above 3400 hg/${\mathrm{cm}}^{2}$ where only the region of larger zenith angles was investigated). The absolute vertical-depth-intensity curve determined solely by this experiment is in general agreement with curves obtained by other authors using data from a variety of sources; however, significant differences can be noted. Comparison of the observed zenithal dependence to theoretical predictions indicates that muons are produced mostly from pion decay, with no evidence for direct muon production. The integral muon energy spectrum at sea level determined from the present underground measurements and Kobayakawa's range-energy relation is in agreement with other experiments, with an exponent $\ensuremath{\beta}=\ensuremath{-}2.45$.