Abstract
The momentum spectrum of muons in the vertical cosmic ray flux at Durham has been measured for the momentum range 0.4-10 GeV/c. The measurements are based on some 191 000 trajectories. The bias introduced by the condition that the particles should be unaccompanied has been studied and found to be small.
The measurements on the momentum spectrum are compared with those of other workers and possible causes of the discrepancies are examined. It is concluded that the relative intensities are known with an accuracy to about 3% over the range 0.4-10 GeV/c.
The production spectrum of cosmic ray pions has been determined under the assumption that the sea-level muons all come from pions. Representing the spectrum as N(pπ) = Apπ-γ, γ is found to be constant and equal to 2.65, for pπ > 5 GeV/c. Below this momentum γ falls continuously and reaches the value 1.93 at a pion momentum of 1 GeV/c. The production spectrum agrees well with those given by Olbert in 1954 and by Puppi in 1956 above 3 GeV/c but has significantly lower intensity at lower momenta.