Measurement of the semileptonic decays ¯¯¯B→Dτ−¯ντ and ¯¯¯B→D∗τ−¯ντ

Abstract

We present measurements of the semileptonic decays B − → D 0 τ − ¯ ν τ , B − → D * 0 τ − ¯ ν τ , ¯¯¯ B 0 → D + τ − ¯ ν τ , and ¯¯¯ B 0 → D * + τ − ¯ ν τ , which are sensitive to non-standard model amplitudes in certain scenarios. The data sample consists of 232 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II e + e − collider. We select events with a D or D ∗ meson and a light lepton ( ℓ = e or μ ) recoiling against a fully reconstructed B meson. We perform a fit to the joint distribution of lepton momentum and missing mass squared to distinguish signal ¯¯¯ B → D ( * ) τ − ¯ ν τ ( τ − → ℓ − ¯ ν ℓ ν τ ) events from the backgrounds, predominantly ¯¯¯ B → D ( * ) ℓ − ¯ ν ℓ . We measure the branching-fraction ratios R ( D ) ≡ B ( ¯¯¯ B → D τ − ¯ ν τ ) / B ( ¯¯¯ B → D ℓ − ¯ ν ℓ ) and R ( D ∗ ) ≡ B ( ¯¯¯ B → D ∗ τ − ¯ ν τ ) / B ( ¯¯¯ B → D ∗ ℓ − ¯ ν ℓ ) and, from a combined fit to B − and ¯¯¯ B 0 channels, obtain the results R ( D ) = ( 41.6 ± 11.7 ± 5.2 ) % and R ( D ∗ ) = ( 29.7 ± 5.6 ± 1.8 ) % , where the uncertainties are statistical and systematic. Normalizing to measured B − → D ( * ) 0 ℓ − ¯ ν ℓ branching fractions, we obtain B ( ¯¯¯ B → D τ − ¯ ν τ ) = ( 0.86 ± 0.24 ± 0.11 ± 0.06 ) % and B ( ¯¯¯ B → D ∗ τ − ¯ ν τ ) = ( 1.62 ± 0.31 ± 0.10 ± 0.05 ) % , where the additional third uncertainty is from the normalization mode. We also present, for the first time, distributions of the lepton momentum, | p ∗ ℓ | , and the squared momentum transfer, q 2 .