Energy Spectra, Altitude Profiles and Charge Ratios of Atmospheric Muons

TL;DR

This study measures atmospheric muon spectra and charge ratios during balloon ascent, comparing results with models and previous data to improve understanding of atmospheric neutrino production.

Contribution

It provides new measurements of muon charge ratios and momentum spectra at various atmospheric depths, highlighting discrepancies with existing models.

Findings

Measured mu- fluxes are up to 70% lower than predictions at shallow depths.

Good agreement between measurements and models at greater depths.

Implications for atmospheric neutrino flux predictions.

Abstract

We present a new measurement of air shower muons made during atmospheric ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio mu+ / mu- is presented as a function of atmospheric depth in the momentum interval 0.3-0.9 GeV/c. The differential mu- momentum spectra are presented between 0.3 and about 50 GeV/c at atmospheric depths between 13 and 960 g/cm^2. We compare our measurements with other recent data and with Monte Carlo calculations of the same type as those used in predicting atmospheric neutrino fluxes. We find that our measured mu- fluxes are smaller than the predictions by as much as 70% at shallow atmospheric depths, by about 20% at the depth of shower maximum, and are in good agreement with the predictions at greater depths. We explore the consequences of this on the question of atmospheric neutrino production.