Evidence of Pair Origin of Prompt Muons

A comparison of measurements of prompt single muons, produced in the forward direction by 400-GeV proton interactions, with the results of measurements of muon pairs produced under the same conditions shows that the pair intensity accounts for the inclusive single-muon flux in a manner which is insensitive to the details of the production and decay of the muon pairs. The mean invariant mass of the pairs is about 900 MeV/${\mathit{c}}^2$.