Measurement of Semileptonic B Decays into Orbitally Excited Charmed Mesons

Abstract

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 Υ ( 4 S ) 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 = m ( D ** ) − m ( D ) distributions. Product branching fractions are determined to be B ( B + → D 0 1 ℓ + ν ℓ ) × B ( D 0 1 → D * + π − ) = ( 2.97 ± 0.17 ± 0.17 ) × 10 − 3 , B ( B + → D * 0 2 ℓ + ν ℓ ) × B ( D * 0 2 → D ( * ) + π − ) = ( 2.29 ± 0.23 ± 0.21 ) × 10 − 3 , B ( B 0 → D − 1 ℓ + ν ℓ ) × B ( D − 1 → D * 0 π − ) = ( 2.78 ± 0.24 ± 0.25 ) × 10 − 3 and B ( B 0 → D * − 2 ℓ + ν 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 → D π − ) / Γ ( D ∗ 2 → D ( * ) π − ) = 0.62 ± 0.03 ± 0.02 .