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Investigation of Semileptonic $B$ Meson Decay to P-Wave Charm Mesons

We have studied semileptonic $B$ meson decays with a P-wave charm meson in the final state using 3.29 x 10^6 B\bar{B} events collected by the CLEO~II detector at the Cornell Electron-positron Storage Ring. We find a value for the exclusive semileptonic product branching fraction: Br(B^- -> D_1^0 l^- \barν) x Br(D_1^0 -> D^{*+}π^-) = (0.373 \pm 0.085 \pm 0.052 \pm 0.024)% and an upper limit for Br(B^- -> D_2^{*0} l^- \barν) x Br(D_2^{*0} -> D^{*+}π^-) < 0.16%$ (90% C.L.). These results indicate that at least 20% of the total B^- semileptonic rate is unaccounted for by the observed exclusive decays, B^- -> D^0 l^- \barν, B^- -> D^{*0} l^- \barν, B^- -> D_1^0 l^- \barν, and B^- -> D_2^{*0} l^- \barν.