The NOMAD Collaboration presents a study of opposite sign dimuon events in
the framework of Leading Order QCD. A total of 2714 neutrino- and 115 antin
eutrino-induced opposite sign dimuon events with E-mu 1, E-mu 2 > 4.5 GeV,
15 < E-nu < 300 GeV and Q(2) > 1 (GeV/c)(2) are observed in the Front-Calor
imeter of NOMAD during the 1995 and 1996 runs. The analysis yields a value
for the charm quark mass of m(c) = 1.3(-0.3-0.3)(+0.3+0.3) GeV/c(2) and fur
the average semileptonic branching ratio of B-c = 0.095(-0.007-0.013)(+0.0
07+0.014). The ratio of the strange to non-strange sea in the nucleon is me
asured to be kappa = 0.48(-0.07-0.12)(+0.09+0.17). The measured rate of cha
rm-induced dimuon relative to single muon, as a function of neutrino energy
, is consistent with the slow rescaling hypothesis of heavy quark productio
n. (C) 2000 Published by Elsevier Science B.V.