In dimuon production $\mu N\to \mu \mu X$ the signal from associated charm production with semileptonic charm decay is likely to be swamped by background from electromagnetic and hadronic trimuons where one muon is lost through small-angle acceptance cuts. However, if the small-angle cut is replaced by a small-angle muon veto, the calculated background drops well below the expected charm dimuon signal. For trimuon production $\mu N\to \mu \mu \mu X$ there is little difference between cut and veto situations; the charm signal is much smaller than background but can be separated by energy and invariant-mass cuts.

• Received 11 September 1979

DOI:https://doi.org/10.1103/PhysRevD.21.299