The positive excess of cosmic ray muons at large zenith angles

Abstract

Details of two solid iron magnetic spectrographs, incorporating neon flash tubes, with m.d.m.'s. of 300 GeV/o and 1950 GeV/c are presented, as are the results on the µ(^+)/µ(^-)ratio in the zenith angular ranges 77.º5 - 90º , and 82.5º - 90º based on samples of 10832 particles and 2167 particles respectively, obtained with these instruments. In the energy region where comparison with the work of other authors can be made agreement obtains. The overall results confirm, in general, previous values below 200 GeV but do not show any great evidence for a sharp minimum in the ratio in the region of 50 - 100 G-eV as reported by some authors. At higher energies the present results do not show a rapidly increasing ratio, as was expected from an extrapolation of earlier measurements. A review of all published measurements on the µ(^+)/µ(^-) ratio is presented, which suggests an approximately constant ratio from E-3 - 10(^3) GeV, of 1,20 - 1.25. In an effort to give a theoretical interpretation of the results it is shown that pion production within the framework of a statistical model based on our knowledge of nucleon interactions at high energies will not account for the experimental data. The effect of, and evidence for, the production of kaons, subject to certain assumptions, is investigated and it is concluded that, under the assumptions considered, the adopted value of the K/π ratio is not sufficient to account for the data in the region Eµ= 10 - 50 G-eV. The effect of other dynamical models such as the isobar model and the O.P,3. model are considered. It is argued that the production of T = 1/2 isobars with a slowly decreasing cross-section, combined with the other features of nucleon interactions as observed at accelerator energies, is sufficient to account for the present experimental position when the errors in the experimental data are taken into account, but none of several proposed models for particle production in high energy interactions can be uniquely selected on the basis of the results.