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

TL;DR

This study developed a specialized spectrometer to measure the low-energy cosmic-ray muon flux below 400 MeV, providing data to validate and improve existing atmospheric models.

Contribution

A novel full-absorption spectrometer with energy degradation techniques was created to measure muons below 75 MeV, filling a gap in low-energy cosmic-ray data.

Findings

The spectrometer successfully measured muon flux below 400 MeV.

Results agree with the PARMA model for low-energy muons.

The method enables accurate low-energy muon flux estimation.

Abstract

Recent applications of cosmic-ray muons require accurate modeling of their flux at low-energy. However, no measurement has been reported below 400 MeV. Therefore, we developed a full-absorption muon energy spectrometer 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 10 and 11 days each. The measurement results were compared with an analytical cosmic-ray model, PARMA (the particle and heavy ion transport code system-based analytical radiation model in the atmosphere) and we found that the model can precisely predict the lower energy part of the flux.