HIGH-ENERGY COSMIC-RAY PHYSICS WITH UNDERGROUND MUONS IN MACRO .2. PRIMARY SPECTRA AND COMPOSITION

Multimuon data from the MACRO experiment at Gran Sasso have been analy zed using a new method, which allows one to estimate the primary cosmi c ray fluxes. The estimated all-particle spectrum is higher and flatte r than the one obtained from direct measurements but is consistent wit h EAS array measurements. The spectral indexes of the fitted energy sp ectrum are 2.56 +/- 0.05 for E < 500 TeV and 2.9 +/- 0.3 for E > 5000 TeV with a gradual change at intermediate energies. The average mass n umber shows little dependence on the primary energy below 1000 TeV, wi th a value of 10.1 +/- 2.5 at 100 TeV. At higher energies the best fit average mass shows a mild increase with energy, even though no defini te conclusion can be reached taking into account errors. The fitted sp ectra cover a range from similar to 50 TeV up to several thousand TeV.