Study of exclusive B→Xuℓν decays and extraction of |Vub| using full reconstruction tagging at the Belle experiment

Abstract

We report the results of a study of the exclusive semileptonic decays B- -> pi(0)l(-)(v) over bar (l), (B) over bar (0) -> pi(+)l(-)(v) over bar (l), B- -> rho(0)l(-)(v) over bar (l), (B) over bar (0) -> rho+l(-)(v) over bar (l) and B- -> omega l(-)(v) over bar (l), 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- -> pi(0)l(-)(v) over bar (l)) = (0.80 +/- 0.08 +/- 0.04 x 10(-4), B((B) over bar (0) -> pi(0)l(-)(v) over bar (l)) = (1.49 +/- 0.09 +/- 0.07) x 10(-4), B(B- -> rho(0)l(-)(v) over bar (l)) = 1.83 +/- 0.10 +/- 0.10 x 10(-4), B((B) over bar (0) -> rho(0)l(-)(v) over bar (l) 3.22 +/- 0.27 +/- 0.24) x 10(-4), and B(B- -> omega l(-)(v) over bar (l)) = 1.07 +/- 0.16 +/- 0.07) x 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 q(2) = (p(l) + p(v))(2), where p(l) and p(v) are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent light cone sum rule calculation, latticeQCDresults and a model-independent description of the hadronic form factor, a value of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar (3.52 +/- 0.29) x 10(-3) is extracted. A structure in the two-pion invariant mass distribution near 1.3 GeV/c(2), which might be dominated by the decay B- -> f(2)(1270)l(-)(v) over bar (l), f(2) -> pi(+)pi(-), is seen. These results are obtained from a 711 fb(-1) data sample that contains 772 x 10(6) B (B) over bar pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider.