The momentum spectrum of cosmic-ray muons at large zenith angles

Abstract

The momentum spectrum of cosmic-ray muons has been measured as a function of zenith angle in the range 77.5°-90° and covering the momentum band 3-500 GeV/c. Based on our knowledge of the experimentally determined muon energy spectrum in the vertical direction, an accurate analysis has been made of the inclined muon spectra expected as a function of the ratio of kaons to pions produced in high energy interactions. Inclusion of the various kaon decay modes reduces the sensitivity of the inclined intensities to the K/π ratio and despite the good statistical accuracy of the present measurements only an upper limit can be set to the ratio, the conclusion being that K/π ⩽ 0.4 at production in the nuclear collisions of high energy nucleons in the energy range 6 × 102-4 × 104 GeV. It is pointed out that an accurate estimate of the ratio will be possible when improved measurements of both the vertical and near-horizontal muon intensities are available in the region of 1000 GeV/c.