000004568 001__ 4568
000004568 005__ 20241022104651.0
000004568 037__ $$aBELLE2-PTHESIS-2024-019
000004568 041__ $$aeng
000004568 100__ $$aKazuki Kojima
000004568 245__ $$aSearch for lepton flavor universality violation in $\overline{B} \rightarrow D^{*}\tau^{-}\overline{\nu}_{\tau}$ decays using hadronic $B$ tagging at the Belle II experiment
000004568 260__ $$aNagoya$$bNagoya University$$c2024
000004568 300__ $$a138
000004568 500__ $$aPresented on 25 03 2024
000004568 502__ $$aPhD$$bNagoya, Nagoya University$$c2024
000004568 520__ $$aIn the standard model of particle physics (SM), lepton flavor universality is an axiom that states that the coupling constants in the interaction between leptons and gauge particles are the same regardless of the lepton flavor $e$, $\mu$, or $\tau$. This universality has been demonstrated by various experiments. On the other hand, in the semi-leptonic $B$ decay, the ratio of the branching fractions $R(D^{(*)}) = \mathcal{B}(\overline{B} \rightarrow D^{(*)}\tau^{-}\overline{\nu}_{\tau}) / \mathcal{B}(\overline{B} \rightarrow D^{(*)}\ell^{-}\overline{\nu}_{\ell})$, where $\ell$ represents an electron or muon, show a tensions with the SM expectations at a significance of $3.2\sigma$. This deviation could be a sign of physics beyond the SM (BSM). We search for lepton flavor universality violation by measuring $R(D^{*})$ using $189~\mathrm{fb}^{-1}$ data collected between 2019 and 2021 at the Belle II experiment. We find \begin{align}     R(D^{*}) = 0.262~{}_{-0.039}^{+0.041}~(\mathrm{stat.})~{}_{-0.032}^{+0.033}~(\mathrm{syst.}). \nonumber \end{align} This result is consistent with the SM predictions. Therefore, no significant violation of lepton flavor universality is observed. The results also agree with the previous measurements within the uncertainty. The world average of the $R(D^{(*)})$ measurements, including our measurement, shows a slight increase in the deviation from the SM prediction from $3.2\sigma$ to $3.3\sigma$. Finally, we discuss possible BSM contributions in $\overline{B} \rightarrow D^{*}\tau^{-}\overline{\nu}_{\tau}$ based on the new world average of $R(D^{(*)})$ and prospects of sensitivity on $R(D^{*})$ at the Belle~II experiment.
000004568 700__ $$aToru Iijima$$edir.
000004568 8560_ $$fkojima@hepl.phys.nagoya-u.ac.jp
000004568 8564_ $$uhttps://docs.belle2.org/record/4568/files/BELLE2-PTHESIS-2024-019.pdf
000004568 980__ $$aTHESIS