Kavli Affiliate: T. Higuchi
| First 5 Authors: Belle II Collaboration, I. Adachi, L. Aggarwal, H. Aihara, N. Akopov
| Summary:
We present a measurement of $|V_{ub}|$ from a simultaneous study of the
charmless semileptonic decays $B^0topi^- ell^+ nu_{ell}$ and $B^+torho^0
ell^+nu_{ell}$, where $ell = e, mu$. This measurement uses a data sample
of 387 million $Boverline{B}$ meson pairs recorded by the Belle~II detector at
the SuperKEKB electron-positron collider between 2019 and 2022. The two decays
are reconstructed without identifying the partner $B$ mesons. We simultaneously
measure the differential branching fractions of $B^0topi^- ell^+ nu_{ell}$
and $B^+torho^0 ell^+nu_{ell}$ decays as functions of $q^2$ (momentum
transfer squared). From these, we obtain total branching fractions
$B(B^0topi^- ell^+ nu_{ell}) = (1.516 pm 0.042 (mathrm{stat}) pm 0.059
(mathrm{syst})) times 10^{-4}$ and $B(B^+torho^0 ell^+nu_{ell}) = (1.625
pm 0.079 (mathrm{stat}) pm 0.180 (mathrm{syst})) times 10^{-4}$. By
fitting the measured $B^0topi^- ell^+ nu_{ell}$ partial branching
fractions as functions of $q^2$, together with constraints on the
non-perturbative hadronic contribution from lattice QCD calculations, we obtain
$|V_{ub}|$ = $(3.93 pm 0.09 pm 0.13 pm 0.19) times 10^{-3}$. Here, the
first uncertainty is statistical, the second is systematic, and the third is
theoretical.
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