Measurement of lepton mass squared moments in B→Xcℓν¯ℓ decays with the Belle II experiment

Le résumé fourni par la source

We present measurements of the first to fourth moments of the lepton mass squared ${q}^{2}$ of $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays for $\ensuremath{\ell}=e$, $\ensuremath{\mu}$ and with ${X}_{c}$ a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance corresponding to $62.8\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity and collected by the Belle II 2 experiment in 2019 and 2020. To identify the ${X}_{c}$ system and reconstruct ${q}^{2}$, one of the $B$ mesons from an $\mathrm{\ensuremath{\Upsilon}}(4S)\ensuremath{\rightarrow}B\overline{B}$ decay is fully reconstructed in a hadronic decay mode using a multivariate $B$ tagging algorithm. We report raw and central moments for ${q}^{2}>1.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$ up to ${q}^{2}>8.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$, probing up to 77% of the accessible $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ phase space. This is the first measurement of moments in the experimentally challenging range of $[1.5,2.5]\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$. The results can be used for a new determination of $|{V}_{cb}|$ using inclusive $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays.

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