Angular distribution of low momentum atmospheric muons at ground level

TL;DR

This study measures the angular distribution of low momentum atmospheric muons at ground level, filling a gap in data for certain geomagnetic cutoff rigidities and providing results consistent with theoretical models.

Contribution

It provides new measurements of muon angular distributions for specific geomagnetic cutoff rigidities, using a novel experimental setup and analysis method.

Findings

Muon flux follows a cos^n(θ) distribution with n=1.88-0.12*P_c^c.

Data fill a gap in geomagnetic cutoff rigidity range 8-14 GV.

Results are consistent with existing literature and models.

Abstract

We report measurements of the angular distributions of low momentum atmospheric muons at 38 m above sea level for zenith angles $\theta$ 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 $\cos^{n}(\theta)$ distribution in good agreement with the literature. These data contribute to fill the gap in the geomagnetic cutoff rigidity interval 8~GV$<P_c<$14~GV where no similar measurements were performed before. We found that $n=1.88-0.12~P_{\mu}^c$ in this domain of muon momenta cutoff $P_{\mu}^c$<1 GeV$/$c. The present measurements are useful for many muon studies requiring an accurate integrated flux.