First observation of the decay $B^0\to \psi (2S){\pi }^0$

We report a measurement of the $B^0\to \psi (2S){\pi }^0$ branching fraction based on the full $\mathrm{\Upsilon }(4S)$ data set of $772\times {10}^6$ $B\overline{B}$ pairs collected by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We obtain $\mathcal{B}(B^0\to \psi (2S){\pi }^0)=(1.17\pm 0.17(\mathrm{stat})\pm 0.08(\mathrm{syst}))\times {10}^{-5}$. The result has a significance of 7.2 standard deviations and is the first observation of the decay $B^0\to \psi (2S){\pi }^0$.

Figure 1

Projections of the fit to the $B^0\to \psi (2S){\pi }^0$ data in the entire fit region onto $M_{\mathrm{bc}}^{\prime }$ (left) and $\mathrm{\Delta }E$ (right). Points with error bars represent the data and the solid black curves represent the fit results. Green hatched curves show the $B^0\to \psi (2S){\pi }^0$ signal component, blue dash-dotted curves show the $c\overline{c}$ background component, and red dotted curves indicate the combinatorial background.

Figure 2

$\mathcal{B}(B^0\to \psi (2S){\pi }^0)$ likelihood scan. The likelihood is convolved with an additive systematic uncertainty.