Angular distribution of low momentum atmospheric muons at ground level

Abstract

We report measurements of the angular distributions of low momentum atmospheric muons at 38 m above sea level for zenith angles θ between -60 and 60 degrees in the south-north direction. The muon detection was performed with two NaI(Tl) scintillation detectors mounted in coincidence. An adjustable lead thickness placed between the detectors allowed to select muons with a minimal momentum ranging from 0.3 to 0.9 GeV/c. The integrated and the differential muon flux were determined by analyzing the deposited energy spectra in the scintillators backed up by a Geant4 simulation of the experimental setup. The results are consistent with the cos n (θ) distribution in good agreement with the literature. These data contribute to fill the gap in the geomagnetic cutoff rigidity interval 8 GV < Pc < 14 GV where no similar measurements were performed before. We found that n = 1.88 - 0.12 Pμ c in this domain of muon momenta cutoff Pμ c < 1 GeV/c. The present measurements are useful for many muon studies requiring an accurate integrated flux.