Determination of |Vcb| from B → Dlν decays at Belle II

Sumitted to PubDB: 2025-01-10

Category: Physics / performance paper

Tags: Run 1

Principal Authors Philipp Horak, Christoph Schwanda
Date 2025-12-16
Working group Semileptonic and Missing Energy Decay
Belle II Number BELLE2-PUB-PH-2025-003
Abstract We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from the decay $B\to D\ellν_\ell$ using a $365~\mathrm{fb}^{-1}$$e^+e^-\toΥ(4S)\to B\bar B$ data sample recorded by the Belle II experiment at the SuperKEKB collider. The semileptonic decay of one $B$ meson is reconstructed in the modes $B^0\to D^-(\to K^+π^-π^-)\ell^+ν_\ell$ and $B^+\to \bar D^0(\to K^+π^-)\ell^+ν_\ell$, where $\ell$ denotes either an electron or a muon. Charge conjugation is implied. The second $B$ meson in the $Υ(4S)$ event is not reconstructed explicitly. Using an inclusive reconstruction of the unobserved neutrino momentum, we determine the recoil variable $w=v_B\cdot v_D$, where $v_B$ and $v_D$ are the 4-velocities of the $B$ and $D$ mesons. We measure the total decay branching fractions to be $\mathcal{B}(B^0\to D^-\ell^+ν_\ell)=(2.06 \pm 0.05\,(\mathrm{stat.}) \pm 0.10\,(\mathrm{sys.}))\%$ and $\mathcal{B}(B^+\to\bar D^0\ell^+ν_\ell)=(2.31 \pm 0.04\,(\mathrm{stat.}) \pm 0.09\,(\mathrm{sys.}))\%$. We probe lepton flavor universality by measuring $\mathcal{B}(B\to Deν_e)/\mathcal{B}(B\to Dμν_μ)=1.020 \pm 0.020\,(\mathrm{stat.})\pm 0.022\,(\mathrm{sys.})$. Fitting the partial decay branching fraction as a function of $w$ and using the average of lattice QCD calculations of the $B\to D$ form factor, we obtain $ |V_{cb}|=(39.2\pm 0.4\,(\mathrm{stat.}) \pm 0.6\,(\mathrm{sys.}) \pm 0.5\,(\mathrm{th.})) \times 10^{-3}$.
ArXiv https://arxiv.org/abs/2506.15256
Inspire https://inspirehep.net/literature/2936544
DOI 10.1103/vs8k-259v
Reference Phys.Rev.D 112, 112009 (2025)
Bibtex 
@article{Belle-II:2025rna,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Determination of |Vcb| using B{\textrightarrow}D{\ensuremath{\ell}}{\ensuremath{\nu}}l decays at Belle II}",
    eprint = "2506.15256",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2025-004, KEK Preprint 2025-1",
    doi = "10.1103/vs8k-259v",
    journal = "Phys. Rev. D",
    volume = "112",
    number = "11",
    pages = "112009",
    year = "2025"
}
Journal Phys.Rev.D

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