L3+C - The atmospheric muon momentum spectrum

The opportunity to improve substantially the precision of the measurement of the cosmic ray muon momentum spectrum is given by the upgrade of the L3 spectrometer located at LEP, CERN, Geneva. Absolute flux results in the momentum range between 20 GeV and 3 TeV are presented for zenith angles ranging from 0° to 58°. The charge ratio is measured from 20 to 500 GeV. A comparison with different experimental data and models is also discussed.