Observation and Measurements of Semileptonic$B$ decays to $D^{**}$ Mesons

Using 460 pb$^{-1}$ of integrated luminosity accumulated with the D\O\ detector, we have observed the semileptonic decays $B \rightarrow \mu \mu D^0_1(2420) X$ and $B \rightarrow \mu \nu D^{*0}_2(2460) X$. The results on their branching rates are presented.