Observation of the Vector Meson Cabibbo Suppressed Decay
D+ --> rho mu nu
by P.L. Frabetti et al.
We report on the first statistically significant observation of the
vector meson Cabibbo suppressed semileptonic decay D+ --> rho mu nu.
We measure the branching ratio with respect to the decay mode
D+ --> K* mu nu to be 0.079 \pm 0.019 \pm 0.013. Data was collected
by Fermilab photoproduction experiment E687.