Measurement of Branching Fraction and Longitudinal Polarization in $B^0\to \ddot{I}{}^{+}\ddot{I}{}^{-}$ Decays at Belle II

Abstract

We present a measurement of the branching fraction and longitudinal polarization of $B^0\to \ddot{I}{}^{+}\ddot{I}{}^{-}$ decays. SuperKEKB electron-positron collision data corresponding to 189~fb${}^{-1}$ of integrated luminosity and containing $198\times 10^{6}B\bar{B}$ pairs collected with the Belle II detector are used. We obtain \begin{eqnarray*} \mathcal{B}(B^0\toρ^+ρ^-) &=& [2.67\pm0.28\,(\mathrm{stat})\,\pm0.28\,(\mathrm{syst})] \times 10^{-5}, \end{eqnarray*} \begin{eqnarray*} f_L &=& 0.956\pm0.035\,(\mathrm{stat})\,\pm 0.033\,(\mathrm{syst}), \end{eqnarray*} These results are consistent with previous measurements and can be used to constrain penguin pollution and to extract the quark-mixing angle $\ddot{I}{•}_2$.