Abstract
The atmospheric muon charge ratio, defined as the number of positive over negative charged muons, is a highly informative observable both for cosmic rays and particle physics. It allows studying the features of high-energy hadronic interactions in the forward region and the composition of primary cosmic rays. In this review results from underground experiments measuring the charge ratio around 1 TeV are discussed. The measurements in the TeV energy region constrain the associated kaon production, which is particularly important e.g. for the calculation of the atmospheric neutrino flux.
Highlights
The atmospheric muon charge ratio is an important observable to shed light on the physics of cosmic ray interactions in atmosphere
The results on the atmospheric muon charge ratio from the CMS, MINOS and OPERA experiments show an increase of R as a function of the vertical surface energy E cos ∗ in the range between a few hundred GeV and a few TeV
The measurements are compatible with a simple parametric model where the rise is due to the increasing kaon contribution to the muon flux
Summary
The atmospheric muon charge ratio is an important observable to shed light on the physics of cosmic ray interactions in atmosphere. In the pion dominated energy region (E 100 GeV), the muon charge ratio R has been measured by several experiments on surface, by balloon-borne detectors and at shallow depths [2] It results to be constant, R 1.27, as expected assuming the validity of Feynman scaling in the fragmentation region [1]. In this work experimental results on the muon charge ratio in the TeV energy range, fundamental to constrain the associated kaon production and test the Feynman scaling in the forward region, are reviewed. This measurement allows to study the chemical composition of cosmic rays near the knee in the primary spectrum.
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