Measurement of Semileptonic B Decays into Orbitally Excited Charmed Mesons

We present a study of B decays into semileptonic final states containing charged and neutral D_1(2420) and D^*_2(2460). The analysis is based on a data sample of 208 fb^(-1) collected at the Y(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. With a simultaneous fit to four different decay chains, the semileptonic branching fractions are extracted from measurements of the mass difference Δ=m(D^(**))-m(D) distributions. Product branching fractions are determined to be B(B^+-->D_1^0ℓ+v_ℓ) x B D^0_1-->D^(*+)π^-) =(2.97±0.17±0.17)×10^(-3), B(B^+-->D^(*0)_2ℓ+v_ℓ)× B(D_2^(*0)-->D^((*)+)π-)=(2.29±0.23±0.21)×10^-3, B(B^0-->D_1^-ℓ+v_ℓ) × B(D_1^--->D^(*0)π^-)=(2.78±0.24±0.25)×10^(-3) and B(B^0-->D_2^(*-)ℓ^+ v_ℓ)× B(D_2^(*-)-->D^((*)0)π^-)=(1.77±0.26±0.11)×10^(-3). In addition we measure the branching ratio Γ(D_2^*-->Dπ^-)/Γ(D_2^*-->D^(*)π^-)=0.62±0.03±0.02.