Precise measurements of cosmic ray spectra at ground level

Abstract

This work describes a series of experiments performed to make an accurate determination of the differential momentum spectrum of cosmic ray muons at ground level in the momentum range 0.3<p<10 GeV/c. The results of measurements on 192,090 single particles passing through the Durham Cosmic Ray Spectrograph are given. The bias resulting from rejection of multiple events has been investigated from 5988 such events recorded and a corrected spectrum derived. The spectrum is used to derive information about nuclear processes at high energy. In particular, an accurate determination is made of the generation spectrum of cosmic ray pions in the atmosphere. It is found that the intensity of pions, I(pπ), of momentum Pπ. may be represented by an equation of the form:- l(pπ)dpπ = A pπ - ɤ dpπ. Where ɤ .2.64, and A is constant for pπ above 4 GeV/c, and is given by the expression. A = 1.82.10(^-4)(pπ/4)0.712 for pπ less than 4 GeV/c. The ratio of positive to negative muons is used to examine the multiplicity of generation of charged pions. The sea-level spectrum has also been used to derive the expected underground depth-intensity relation - this is found to be in good agreement with that directly measured, indicating that the assumed form of energy loss of muons is correct.