Properties of cosmic rays incident in the near-horizontal direction

Abstract

The Durham 'horizontal spectrograph' Mark II has been used to measure the momentum spectrum and the charge ratio of Cosmic-ray muons in the zenith angle range 82.5 - 90 to about 2000 GeV and the results are based on a sample of 3918 particles. By comparing the measured spectra with those predicted from the measured vertical spectrum, for different values of the K/π ratio, a value of 0.42 ± 0.20 has been derived for the K/π ratio in the muon energy range at production, 100 - 2000 GeV, corresponding to3 5primary energy range of ~3.10(^3) – 10(^5) GeV. When comparison is made with the k/π ratios determined by other indirect methods it is concluded that there is no evidence against a near-constant ratio over the wide primary energy range 10(^2) – 10(^6) covered by all methods and that the average value is 0.35 ± 0.20 over this energy range. The present results confirm the results of other authors on the existence of an appreciable charge excess up to energies of at least a few hundred GeV. The present results suggest that at the largest zenith angles there is a maximum in the charge ratio in the energy region 50 - 100 GeV, a feature which does not confirm the minimum in the same energy region, but at somewhat smaller zenith angles, reported by some other workers. The reason for the appearance of the maximum is not known despite strenuous efforts to explain it. At higher energies, one cannot say, sue to the considerable errors in all the data, that there is disagreement between the present result and other data and neither an increase or decrease in the ration is ruled out. The interaction of the incident particles (hitherto assumed to be muons) has been studied from the point of view of identification of the particles. It is shown that the results can be interpreted in terms of the known electromagnetic interactions of muons and the conclusion arrived at is that there is no evidence for the existence of an appreciable flux of the so-called X – particles that could be contaminating the incident muon beam.