Dimuon production in 15.5-GeV/cπpinteractions and the observation of a low-mass continuum

We report the results of an experiment which examines the entire final state of events in which muon pairs were produced in 15.5-GeV/c ..pi../sup + -/p interactions. A portion of this data was presented earlier. Here we report on the final data sample of 890 events obtained from a total of 2.5 x 10/sup 8/ interactions (a sensitivity of (8.65 events/nb) x trigger efficiency). The experiment was sensitive primarily to the low-mass region and the good mass resolution made it possible to identify the contributions from the rho and ..omega.. decays and the eta and ..omega.. Dalitz decays. An excess of events is observed in the dimuon mass region approx.400 -- 600 MeV which is not accounted for by the above-mentioned decays. The final states were examined to search for characteristic differences from those in events without dimuons.