High energy muon number spectrum detected at the Baksan Underground Scintillation Telescope

Integral muon number spectrum has been measured at the Baksan Underground Scintillation Telescope (BUST) for near vertical directions (θ≤20o, effective muon threshold energy is 230 GeV). The analyzed range of the number of muon tracks crossing BUST is 2 - 170. It corresponds to the primary energy range 3.1013 eV-1016 eV. Muon number spectrum calculations have been carried out for different primary compositions. For EAS simulations CORSIKA code (v.6.030, QGSJET01 model) has been used. Our data agree with a composition lighter than the standard one before the knee with the knee position at Z.2.0.1015 eV