Search for the dark photon in B0 ? A?A?, A? ? e+e?, ?+??, and ?+?? decays at Belle

We present a search for the dark photon $A^{\prime}$ in $B^0 \to A^{\prime} A^{\prime}$ decays, where subsequently decays to $e^+ e^-$, $\mu^+ \mu^-$, and $\pi^+ \pi^-$. The is performed by analyzing $772 \times 10^6$ $B\overline{B}$ events collected Belle detector at KEKB e^-$ energy-asymmetric collider $\Upsilon (4S)$ resonance. No signal found mass range $0.01~\mathrm{GeV}/c^2 \le m_{A^{\prime}} 2.62~\mathrm{GeV}/c^2$, we set upper limits of branching fraction 90\% confidence level. products fractions, $\mathcal{B}(B^0 A^{\prime}) \mathcal{B}(A^{\prime} e^+ e^-)^2$ \mu^+ \mu^-)^2$, have order $10^{-8}$ depending on mass. Furthermore, considering decay rate each pair charged particles, A^{\prime})$ are $10^{-8}$-$10^{-5}$. From A^{\prime})$, obtain Higgs portal coupling assumed couplings $10^{-2}$-$10^{-1}$ $m_{h'} \simeq m_{B^0} \pm 40~\mathrm{MeV}/c^2$ $10^{-1}$-$1$ 3~\mathrm{GeV}/c^2$.