Measurement of cosmic-ray spectra with the BESS/BESS-TeV

In order to study neutrino oscillation phenomena using atmospheric neutrinos, it is crucially important to calculate their absolute fluxes and spectral shapes accurately. Absolute flux of primary cosmic ray is the most fundamental information for the calculation. Since production and decay processes of muons are accompanied by neutrino production, observation of atmospheric muons gives fundamental information about atmospheric neutrinos. Our measurement of primary and atmopspheric cosmic rays at various sites with the BESS/BESS-TeV spectrometer will help to improve the accuracy of atmospheric neutrino calculations.