Measurement of lepton mass squared moments in $B \to X_c \ell^+ \bar{\nu}{}_{\ell}$ decays with the Belle II experiment

Abstract We present measurements of the first to fourth moments of the lepton mass squared $q^2$ of \mbox{$B \to X_c \, \ell\, \bar \nu_{\ell}$} decays for $\ell = e, \mu$ and with $X_c$ a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the $\Upsilon(4S)$ resonance corresponding to $62.8 \, \mathrm{fb}^{-1}$ of integrated luminosity and collected by the Belle II experiment in 2019 and 2020. To identify the $X_c$ system and reconstruct $q^2$, one of the $B$ mesons from an $\Upsilon(4S) \to B \kern 0.18em\overline{\kern -0.18em B}$ decay is fully reconstructed in a hadronic decay mode using a multivariate $B$ tagging algorithm. We report raw and central moments for $ q^2 > 1.5 \; \mathrm{GeV^2/c^4}$ up to $q^2 > 8.5 \; \mathrm{GeV^2/c^4}$, probing up to 77% of the accessible \mbox{$B \to X_c \, \ell\, \bar \nu_{\ell}$} phase space. This is the first measurement of moments in the experimentally challenging range of $[ 1.5, 2.5 ] \, \mathrm{GeV^2/c^4}$.
Tags
Working group Semileptonic and Missing Energy Decay
Principal authors @  Florian Bernlochner, Maximilian Welsch
Reference Phys.Rev.D 107, 072002 (2023), DOI: 10.1103/PhysRevD.107.072002
Document BELLE2-PUB-PH-2021-002
Links arXiv:2205.06372, Inspire, PRD
Bibtex 
@article{Belle-II:2022evt,
    author = "Abudin{\'e}n, F. and others",
    collaboration = "Belle-II",
    title = "{Measurement of lepton mass squared moments in B{\textrightarrow}Xc{\ensuremath{\ell}}{\ensuremath{\nu}}{\textasciimacron}{\ensuremath{\ell}} decays with the Belle II experiment}",
    eprint = "2205.06372",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    doi = "10.1103/PhysRevD.107.072002",
    journal = "Phys. Rev. D",
    volume = "107",
    number = "7",
    pages = "072002",
    year = "2023"
}