Measurement of the branching fraction and $CP$ asymmetry in $B^{0} \to π^{0}π^{0}$ decays, and an improved constraint on $φ_{2}$
hep-ex
/ Authors
The Belle Collaboration, T. Julius, M. E. Sevior, G. B. Mohanty, I. Adachi, H. Aihara, S. Al Said, D. M. Asner, V. Aulchenko, T. Aushev
and 176 more authors
R. Ayad, V. Babu, I. Badhrees, A. M. Bakich, V. Bansal, E. Barberio, M. Barrett, M. Berger, V. Bhardwaj, B. Bhuyan, J. Biswal, T. Bloomfield, A. Bobrov, A. Bondar, G. Bonvicini, A. Bozek, M. Bračko, T. E. Browder, D. Červenkov, M. -C. Chang, Y. Chao, V. Chekelian, A. Chen, B. G. Cheon
/ Abstract
We measure the branching fraction and $CP$ violation asymmetry in the decay $B^{0}\to π^{0}π^{0}$, using a data sample of $752\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The obtained branching fraction and direct $CP$ asymmetry are $ \mathcal{B}(B\to π^{0}π^{0}) = [1.31 \pm 0.19~ \text{(stat.)} \pm 0.19~ \text{(syst.)}] \times 10^{-6}$ and $ A_{CP} = +0.14 \pm 0.36~ \text{(stat.)} \pm 0.10~ \text{(syst.)}, $ respectively. The signal significance, including the systematic uncertainty, is 6.4 standard deviations. We combine these results with Belle's earlier measurements of $B^{0}\to π^{+} π^{-}$ and $B^{\pm} \to π^{\pm} π^{0}$ to exclude the $CP$-violating parameter $φ_{2}$ from the range $15.5^{\circ} < φ_{2} < 75.0^{\circ}$ at 95\% confidence level.