Improved measurement of $B^0\to {\pi }^0{\pi }^0$

Abstract

We report an improved measurement of the decay $B^0\to {\pi }^0{\pi }^0$, using a data sample of 535 $\times 10^{6}B\bar{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider. The measured branching fraction is $\mathcal{B}(B^0\to {\pi }^0{\pi }^0)=1.1\pm 0.3(stat.)\pm 0.1(syst.)$, with a significance of 5.4 standard deviations including systematic uncertainties. We also report the partial rate asymmetry: $\acp(B^0 \to π^0 π^0)$ = 0.44 ${}_{-0.62}^{+0.73}$(stat.)${}_{-0.06}^{+0.04}$(syst.).

arXiv comment10pages,3 figures