A new measurement of the muon component in the atmosphere

We report new measurements of the muon charge ratio in the atmosphere from the data collected by the CAPRICE98 balloon-borne magnet spectrometer during the ascent of the payload. The measurement was performed starting from Ft. Sumner, NM at a vertical rigidity cutoff of about 4.5 GV on May 28, 1998. The results are reported separately in three momentum bins, in none of which significant dependences on altitude have been found. The charge ratio below 1 GeV/c measured in this experiment is in agreement with previous results from experiments at comparable latitudes, and lower than measurements at low geomagnetic cutoff, which may point out latitude-dependent effects. This is the first time that the muon charge ratio has been investigated from ground level down to residual atmospheric depths of 5 g/cm at particle momenta larger than 2 GeV/c.