Muon-Pair Separation Measurements and Comparison with Transverse-Momentum Models

Rates of high-energy cosmic-ray muon pairs have been measured for separations up to 70 m. Detailed calculations imply that the mean transverse momentum $〈p_T〉$ of mesons with $x>\mathrm{}0.01\mathrm{}$ is 0.66 ± 0.10 GeV/c at laboratory energies of ≳ 10 000 GeV. We find that the high-$p_T$ muons result mostly from decay of abundantly produced particles with lifetimes ≳ ${10}^{-8\mathrm{}}$ sec, such as pions and kaons.