Angular distributions of muon pairs produced by 194 GeV/c negative pions

We present the angular distributions of muon pairs obtained in a high-statistics experiment using a 194-GeV/c π^- impinging on a tungsten target. Our results are based on the analysis of 145,000 events with positive Feynman x and mass above 4.07 GeV/c², excluding the ϒ region. Simple first-order QCD relations allow us to determine the ratio of annihilation with hard-gluon emission to the sum of annihilation with hard-gluon emission and hard-gluon Compton scattering, which is found to be about 58% to 75%. We determine the parton square intrinsic transverse momenta to be of the order of 0.6 (GeV/c)², and about 30% larger in the pion than in the nucleon. At large x ₁, our data agree with the higher-twist hypothesis, and support the interpretation of the relevant scale parameter as the dimuon square transverse momentum.