Measurement of energy differential spectrum of cosmic-ray muons below 400 MeV

Abstract

Abstract Recent applications of cosmic-ray muons require accurate modeling of their flux at low energy. However, only a few measurements have been reported below 400 MeV. Therefore, we developed a full-absorption muon energy spectrometer (FAMES) to obtain energy differential flux below 400 MeV. Because our main detector can measure muon energies below 75 MeV, an energy degradation method is adopted (using 5- and 20-cm thick lead blocks) to shift the sensitive energy range. Three measurements were performed (in the normal mode and the two energy degrading modes) for around two weeks. The measurement results were compared with PARMA, an analytical model for estimating terrestrial cosmic-ray fluxes nearly anytime and anywhere in the world. As a result, we found that the model can precisely predict the flux except its lower energy part.