F. Abudinén ; P.-T. Chang ; Y.-C. (Janice) Chen ; E. Ganiev ; C.-H. Li ; R. Manfredi ; H.-G. Moser ; S. Raiz ; M. Reif ; D. Tonelli ; B. Wach

20 September 2020

Abstract: We report on first measurements of branching fractions~($\mathcal{B}$) and CP-violating charge asymmetries~($\mathcal{A}_{\rm CP}$) in charmless $B$ decays at Belle~II. We use a sample of electron-positron collisions collected in 2019 and 2020 at the $\Upsilon(4S)$ resonance and corresponding to $34.6$\,fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $\Delta E$ distributions of the resulting samples, restricted in $M_{\rm bc}$, are fit to determine signal yields ranging from 35 to 450 decays for the channels \mbox{$B^0 \to K^+\pi^-$}, \mbox{$B^+ \to K^+\pi^0$}, \mbox{$B^+ \to \PKzS\pi^+$}, \mbox{$B^0 \to \PKzS\pi^0$}, \mbox{$B^0 \to \pi^+\pi^-$}, \mbox{$B^+ \to \pi^+\pi^0$}, \mbox{$B^+ \to K^+K^-K^+$}, and \mbox{$B^+ \to K^+\pi^-\pi^+$}. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain the following results: \begin{center} $\mathcal{B}(B^0 \to K^+\pi^-) = [18.9 \pm 1.4(\rm stat) \pm 1.0(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^+ \to K^+\pi^0) = [12.7 ^{+2.2}_{-2.1} (\rm stat)\pm 1.1(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^+ \to K^0\pi^+) = [21.8 ^{+3.3}_{-3.0}(\rm stat) \pm 2.9(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^0 \to K^0\pi^0) = [10.9^{+2.9}_{-2.6} (\rm stat)\pm 1.6(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^0 \to \pi^+\pi^-) = [5.6 ^{+1.0}_{-0.9}(\rm stat) \pm 0.3(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^+ \to \pi^+\pi^0) = [5.7 \pm 2.3 (\rm stat)\pm 0.5(\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^+ \to K^+K^-K^+) = [32.0 \pm 2.2(\rm stat.) \pm 1.4 (\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{B}(B^+ \to K^+\pi^-\pi^+) = [48.0 \pm 3.8 (\rm stat)\pm 3.3 (\rm syst)]\times 10^{-6}$, \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^0 \to K^+\pi^-) = 0.030 \pm 0.064 (\rm stat) \pm 0.008(\rm syst)$, \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^+ \to K^+\pi^0) = 0.052 ^{+0.121}_{-0.119} (\rm stat)\pm 0.022(\rm syst)$, \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^+ \to K^0\pi^+) = -0.072 ^{+0.109}_{-0.114}(\rm stat) \pm 0.024(\rm syst)$, \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^+ \to \pi^+\pi^0) = -0.268 ^{+0.249}_{-0.322} (\rm stat)\pm 0.123(\rm syst)$, \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^+ \to K^+K^-K^+) = -0.049 \pm 0.063(\rm stat) \pm 0.022 (\rm syst)$, and \end{center} \begin{center} $\mathcal{A}_{\rm CP}(B^+ \to K^+\pi^-\pi^+) = -0.063 \pm 0.081 (\rm stat)\pm 0.023(\rm syst)$. \end{center} These are the first measurements in charmless decays reported by Belle~II. Results are compatible with known determinations and show detector performance comparable with the best Belle results offering a reliable basis to assess projections for future reach.

Keyword(s): Charmless, Phase 3, CP violation
Note: Prepared for ICHEP2020