Observation of wrong-sign tri-muon events in 250 GeV muon-nucleon interactions

Abstract Two trimuon events of the type μ + N→ μ + μ + μ + X and one μ + N→ μ + μ − μ − X have been observed in 250 GeV μ + -iron interactions. The expected rate from the decay of hadrons (charm, π , K) is about one event. Other processes that may contribute are both beauty production and charm production with D 0 − D 0 mixing. The data give upper limits of 12×10 −36 cm 2 for the cross section of beauty pair production by muons, and 20% for D 0 ↔ D 0 transitions due to mixing, both at 90% confidence level.