Evidence for $B^0 \to \pi^0 \pi^0$

We report evidence for the decay $B^0 \to \pi^0 \pi^0$. The analysis is based on a data sample of 152 million $B\bar{B}$ pairs collected at the $\Upsilon(4s)$ resonance with the Belle detector at the KEKB $e^+ e^-$ storage ring. We find $25.6^{+ 9.3}_{-8.4}(stat)^{+1.6}_{-1.4}(syst)$ $B^0 \to \pi^0 \pi^0$ signal events with a significance of 3.4 standard deviations. We measure the branching fraction to be ($1.7 \pm 0.6 (stat) \pm 0.2 (syst))*10^{-6}$.