Determination of $|{V}_{ub}|$ from Measurements of the Inclusive Charmless Semileptonic Partial Rates of $B$ Mesons using Full Reconstruction Tags

Determination of $| V_{u b} |$ from Measurements of the Inclusive Charmless Semileptonic Partial Rates of $B$ Mesons using Full Reconstruction Tags

I. Bizjak et al. (Belle Collaboration)

Phys. Rev. Lett. 95, 241801 – Published 8 December 2005

Abstract

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element $| V_{u b} |$ , based on $253 {fb}^{- 1}$ of data collected by the Belle detector at the KEKB $e^{+} e^{-}$ asymmetric collider. Events are tagged by fully reconstructing one of the $B$ mesons, produced in pairs from $Υ (4 S)$ . The signal for $b \to u$ semileptonic decay is distinguished from the $b \to c$ background using the hadronic mass $M_{X}$ , the leptonic invariant mass squared $q^{2}$ and the variable $P_{+} \equiv E_{X} - | {\vec{p}}_{X} |$ . The results are obtained for events with $p_{ℓ}^{*} \geq 1 GeV / c$ , in three kinematic regions (1) $M_{X} < 1.7 GeV / c^{2}$ , (2) $M_{X} < 1.7 GeV / c^{2}$ combined with $q^{2} > 8 {GeV}^{2} / c^{2}$ , and by (3) $P_{+} < 0.66 GeV / c$ . The matrix element $| V_{u b} |$ is found to be $(4.09 \pm 0.19 \pm {0.20}_{- 0.15}^{+ 0.14} \pm 0.18) \times 10^{- 3}$ , where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.