Pion-to-proton ratio for unaccompanied high-energy cosmic-ray hadrons at mountain altitude using transition-radiation detector

A transition-radiation (TR) detector, consisting of 24 modules of styrofoam radiators and multiwire proportional chambers, and an ionization calorimeter have been used to measure the pion-to-proton ratio among the unaccompanied cosmic-ray hadrons at a mountain altitude of 730 g ${\mathrm{cm}}^{-2\mathrm{}}$. Using the characteristics of the TR detector obtained from calibrations with particle beams at accelerators, the $\frac{\pi }{p}$ ratio has been determined for cosmic-ray hadrons as $\frac{\pi }{p}=0.96\mathrm{}\pm 0.15$ for hadron energy = 400-800 GeV, and $\frac{\pi }{p}=0.45\mathrm{}\pm 0.25$ for energy > 800 GeV. Monte Carlo simulations of hadron cascades in the atmosphere using the approximate criterion of unaccompaniment suggest that the observed $\frac{\pi }{p}$ ratio as well as the previously reported neutral-to-charge ratio can be understood by assuming a value of about $\frac{1}{3}$ for the charge exchange in nucleon-air-nucleus inelastic interactions at energies above 400 GeV.