Interpretation of the Underground Muon Charge Ratio

TL;DR

This paper analyzes the rise in underground muon charge ratio observed by MINOS, relating it to atmospheric meson production ratios and examining factors affecting the measurement, including energy dependence and primary cosmic ray composition.

Contribution

It introduces a focus on the variable $ ext{E}_{ ext{cos}}$ for studying charge ratios and compares simple parameterizations with detailed simulations and calculations.

Findings

The charge ratio increase is better studied using $ ext{E}_{ ext{cos}}$ rather than $ ext{E}_{ ext{mu}}$.

Energy dependence and primary composition significantly influence the charge ratio.

Neglected effects like dE/dx and heavy primaries impact the interpretation of data.

Abstract

The MINOS experiment has observed a rise in the underground muon charge ratio $r_\mu$ = ${\mu^+/\mu^-}$. This ratio can be related to the atmospheric production ratios of ${\pi^+/\pi^-}$ and ${K^+/K^-}$. Our analysis indicates that the relevant variable for studying the charge ratio+ $\ecos$, rather than $\emu$. We compare a simple energy dependent parameterization of the rise in the charge ratio with more detailed previously published Monte Carlo simulations and an analytical calculation. We also estimate the size of two previously neglected effects in this context: the charge sign dependency of the dE/dx in rock, and the energy dependence of heavy primaries on the derived ${K^+/K^-}$ ratio.