Upper limits on D0-D0 mixing and BB production from muon-nucleon scattering

In deep inelastic interactions of 200 GeV muons with a carbon target, we have found 17 events of the type μ ± N→ μ ± μ ∓ μ ∓ X (“wrong-sign” dimuons). We derive upper limits of 1.2% (90% CL) on D 0 - D 0 transitions (mixing) or, alternatively, of 9 pb (90% CL) cross section for B B pair production as possible sources of such events.