New Measurement of BR(D+ ->Rho0 Mu+ Nu) / BR(D+ ->K*0 Mu+ Nu) Branching Ratio

Using data collected by the FOCUS experiment at Fermilab, we present a new measurement of the charm semileptonic branching ratio BR(D+ -> rho0 mu+ nu)/BR(D+ -> K*0 mu+ nu). From a sample of 320+-44 and 11372+-161 D+ -> rho0 mu+ nu and D+ -> K*0 mu+ nu events respectively, we find BR(D+ -> rho0 mu+ nu)/BR(D+ -> K*0 mu+ nu)=0.041+-0.006(stat)+-0.004(syst).