ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2013, vol. 88, p. -
Study of exclusive B→Xuℓν decays and extraction of |Vub| using full reconstruction tagging at the Belle experiment
We report the results of a study of the exclusive semileptonic decays B-→π0ℓ-ν̄ℓ, B ̄0→π+ℓ -ν̄ℓ, B-→ρ0ℓ -ν̄ℓ, B̄0→ρ +ℓ-ν̄ℓ and B -→ωℓ-ν̄ℓ, where ℓ represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are B(B-→π0ℓ -ν̄ℓ)=(0.80±0.08±0.04) ×10-4, B(B̄0→π+ℓ -ν̄ℓ)=(1.49±0.09±0.07) ×10-4, B(B-→ρ0ℓ -ν̄ℓ)=(1.83±0.10±0.10) ×10-4, B(B̄0→ρ+ℓ -ν̄ℓ)=(3.22±0.27±0.24) ×10-4, and B(B-→ωℓ -ν̄ℓ)=(1.07±0.16±0.07) ×10-4, where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. We also determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q2=(pℓ+p ν)2, where pℓ and pν are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent light cone sum rule calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the Cabibbo-Kobayashi- Maskawa matrix element |Vub|=(3.52±0.29)×10-3 is extracted. A structure in the two-pion invariant mass distribution near 1.3 GeV/c2, which might be dominated by the decay B-→f 2(1270)ℓ-ν̄ℓ, f 2→π+π-, is seen. These results are obtained from a 711 fb-1 data sample that contains 772×106 BB̄ pairs, collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. © 2013 American Physical Society.