Measurements of the μ+/(μ-) Ratio of Cosmic Rays Muons with a Compact Detector Device

A compact device of 10 modules, each consisting of 1 cm lead, 3 cm plastic scintillator and 1 cm aluminum is set up. Cosmic ray muons with primary energies in the range 0.4 ÷ 0.9 GeV and incident angles up to 50° are stopped and decay in the device. Positive muons stopped in the different layers decay with their free life time of 2.2 μs, while the negative muons are captured by the atoms and build muonic atoms. Their reduced life time in these systems, i.e. 0.88 μs in aluminum, is measured by a dedicated multiple time digitizer. An analysis of the combined decay spectrum on the basis of a Monte Carlo simulation using the GEANT code leads to the μ⁺/ μ^- ratio of 1.20 ± 0.06 for a mean muon energy of 0.52 GeV.