Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV

The absolute muon flux between 20 and 3000 GeV was measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 0 to 58 0 . Due to the large exposure of about 150 m 2 sr d and the excellent momentum resolution of the L3 muon chamber system, the muon flux was determined with a precision of 2.3 % at 150 GeV in the vertical direction. The ratio of positive to negative muons was studied between 20 and 500 GeV. The average vertical muon charge ratio is found to be 1.285 ± 0.003 (stat.)± 0.019 (sys.)