The charge ratio of atmospheric muons below 1.0 GeV c(-1) by measuring thelifetime of muonic atoms in aluminium

The compact scintillator device WILLI, set up in IFIN-HH Bucharest (44 degr ees 26' N latitude and 26 degrees 04' E longitude), has been used for measu rements of the charge ratio in the atmospheric muon flux. The experimental method, based on the observation of the reduced effective lifetime of negat ive muons stopped in matter, as compared with the lifetime of positive muon s, gives accurate results and avoids some difficulties and systematic error s of magnetic spectrometers. The studies are focused on an energy range of the muons which provides relevant information for the discussion of the atm ospheric neutrino anomaly and for studies of the atmospheric neutrino and a ntineutrino fluxes. From several measurements at momenta below 1 GeV c(-1), a decrease of the muon charge ratio from 1.30 (at 0.87 GeV c(-1)) to 1.15 (at 0.20 GeV c(-1)) has been found.