The momentum spectrum and charge ratio of cosmic ray muons in the vertical direction between 200 and 5000 GeV/c

Abstract

The sea-level vertical muon momentum spectrum and charge ratio have been measured in the momentum range 200 GeV/c to 3000 GeV/c using the MARS spectrograph at Durham. The analysis of approximatley 80,000 muons is described, and the various instrumental effects which affect the shape or absolute intensity of the spectrum are discussed in detail. Muons accompanied and unaccompanied by extensive air showers are included in the measurement of the muon spectrum. A simple muon production and propogation model has been used to predict the pion and kaon production spectra from the present measurement of the muon spectrum. It has not been possible to predict the proportion of kaons and pions produced in primary cosmic ray interactions in the atmosphere. The present measurement of the muon spectrum is in good agreement with the shape and absolute intensity of the previous measurement of the muon spectrum using the MARS spectrograph (Ayre et al, 1975). :The prediction by Whalley (1974) of a flatter pion and kaon spectrum above 100 GeV/c is substantiated. The shape of the present measurement of the muon spectrum is in agreement, within the limits of statistical accuracy, with the results from other spectrographs, but there are differences in absolute intensity. Comparisons with indirect measurements of the muon spectrum show that the present spectrum is flatter and higher in intensity above 1 TeV/c. The overall value of the charge ratio of muons between 100 GeV/c and 3000 GeV/c is 1.305 ± 0.015. There is an indication of a slight rise of the charge ratio with momentum. This result is consistant with the previous measurement of the charge ratio between 20 and 500 GeV/c using using the MARS spectrograph (Baxendale et al, 1975) and with the results of Ashley et al (1975) above J TeV/c,