Measurement of the branching fraction for $B^{0} \rightarrow \pi^{0} \pi^{0}$ decays reconstructed in 2019-2020 Belle II data

TL;DR

This paper reports the first measurement of the $B^{0} o c0c0$ decay at Belle II, using 2019-2020 data, finding a branching ratio consistent with previous results and demonstrating detector capabilities for future CP violation studies.

Contribution

First reconstruction and measurement of the $B^{0} o c0c0$ decay mode at Belle II with early data, showcasing detector performance and potential for future physics analyses.

Findings

Branching ratio measured as (0.98^{+0.48}_{-0.39} ext{(stat)} ext{+} 0.27 ext{(syst)}) imes 10^{-6}

Signal significance of 3.4 standard deviations

Results consistent with previous measurements

Abstract

We report the first reconstruction of the $B^{0} \to \pi^{0} \pi^{0}$ decay mode at Belle II using samples of 2019 and 2020 data that correspond to 62.8 fb$^{-1}$ of integrated luminosity. We find $14.0^{+6.8}_{-5.6}$ signal decays, corresponding to a significance of 3.4 standard deviations and determine a branching ratio of $\mathcal{B}(B^{0} \rightarrow \pi^{0} \pi^{0}) = [0.98^{+0.48}_{-0.39} \pm 0.27] \times 10^{-6}$. The results agree with previous determinations and contribute important information to an early assessment of detector performance and Belle II's potential for future determinations of $\alpha/\phi_2$ using $B \rightarrow \pi \pi$ modes.