Measurements of Partial Branching Fractions for Bbar --> X_u ell nubar and Determination of |V_{ub}|

TL;DR

This paper measures partial branching fractions of charmless semileptonic B decays and determines |V_{ub}| using a large data sample, multiple phase space regions, and theoretical models to improve understanding of CKM matrix elements.

Contribution

It provides new measurements of partial branching fractions in various phase space regions and extracts |V_{ub}| with multiple theoretical approaches, enhancing precision in CKM matrix element determination.

Findings

Partial branching fractions measured in three phase space regions.

|V_{ub}| values extracted using different theoretical calculations.

Results improve the precision of CKM matrix element |V_{ub}|.

Abstract

We present partial branching fractions for inclusive charmless semileptonic B decays Bbar --> X_u ell nubar, and the determination of the CKM matrix element |V_{ub}|. The analysis is based on a sample of 383 million Y(4S) decays into B Bbar pairs collected with the BaBar detector at the PEP-II e+ e- storage rings. We select events using either the invariant mass M_X of the hadronic system, the invariant mass squared, q^2, of the lepton and neutrino pair, the kinematic variable P_+ or one of their combinations. We then determine partial branching fractions in limited regions of phase space: Delta B = (1.18 +- 0.09_{stat.} +- 0.07_{syst.} +- 0.01_{theo.}) x 10^{-3} (M_X < 1.55 GeV/c^2), Delta B = (0.95 +- 0.10_{stat.} +- 0.08_{syst.} +- 0.01_{theo.}) x 10^{-3} (P_+ < 0.66 GeV/c), and Delta B = (0.81 +- 0.08_{stat.} +- 0.07_{syst.} +- 0.02_{theo.}) x 10^{-3} (M_X < 1.7 GeV/c^2, q^2 > 8 GeV^2/c^4). Corresponding values of |V_{ub}| are extracted using several theoretical calculations.