The charge excess and momentum spectrum of cosmic ray muons in the vertical direction

Abstract

The charge excess and momentum spectrum of cosmic ray muons have been measured at 60 m above sea-level by means of the "Vertical Durham Spectrograph" which had been modi-fied in many respects (e.g. by the addition of a solid iron plug of thickness 45 cm) and re-aligned and calibrated. The effect of the multiple scattering in the magnet is found to be the most serious limitation of the instrument and methods of coping with it are investigated, among others a new statistical method. The values obtained for the charge ratio are 1.240 + 0.036 at 12 GeV/c, 1.262 + 0.031 at 23 GeV/c, 1.279 + 0.038 at 31 GeV/c, 1.208 + O.O69 at 47 GeV/c, 1.269 + u.085 at 66 GeV/c, and 1.324 + 0.111 at 102 GeV/c. These results have been combined with the results of previous workers. The best estimates thus obtained are compared with the theoretical expectations calculated by kacKeown et al. (1965a). The expectations are calculated for an empirical model of nuclear interactions including kaons, for the isobar model (Peters, 1963; Yash Pal, I963), and for the peripheral collision model (Narayan, 1964; Crossland and Powler, 1965), including the empirical low-energy pionization in the two latter models. A qualitative agreement is found between the experiments and theory in each case but quantitative conclusions cannot be drawn because of the statistical errors of the experimental results and because of uncertainty in the parameters of the models. The momentum spectrum observed agrees well with the spectrum given by Osborne et al. (1964) within the accuracy of the instrument. The underground muon spectrum observed by Vernov et al. (1965) and the spectrum of primary nuclei measured by the satellite Proton I (Grigorov et al., 1965; Vernov, 1965) disagree with the present results.