Angular distributions of muon pairs produced by negative pions on deuterium and tungsten

Abstract

We present the angular distributions of high-mass muon pairs produced in a high-statistics experiment by 140 and 194 GeV/c π− beams impinging on a tungsten target, and by 286 GeV/c π− beam on deuterium and tungsten targets. We find no evidence for a center-of-mass energy dependence or a nuclear dependence of the angular distribution parameters. The two parameters λ and μ are found to be essentially independent of any kinematical variable. In contrast, the parameterv increase with the dimuon transverse momentumP T , at variance with recent perturbative QCD predictions. Our statistics at largex 1 are insufficient to substantiate the highertwist prediction.