The charge ratio of the atmospheric muons as probe for azimuthal asymmetry

The charge ratio of the atmospheric muons is a quantity sensitive to hadronic interactions of cosmic rays and to the influence of the geomagnetic field. Experimental information is of current interest for tuning models used for the calculation of atmospheric neutrino fluxes. We report about experimental studies of the charge ratio based on the observation of the lifetime of the muons stopped in the absorber layers (aluminum support) of the detector WILLI, mounted in a rotatable frame and installed in IFIN-HH Bucharest (vertical geomagnetic cut-off rigidity of 5.6 GV). Measurements of the asymmetry of the muon charge ratio in the east-west direction, observed with a mean zenithal angle of 35◦, results in values of the asymmetry of the charge ratio decreasing from 0.25 to 0.20 in the muon momentum range of 0.35-0.50 GeV/c, relevant to the atmospheric neutrino anomaly.