Search for the dark photon in $B^0\to A^{\prime }{A}^{\prime }$, $A^{\prime }\to e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, and ${\pi }^{+}{\pi }^{-}$ decays at Belle

Abstract

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

15 pages, 7 figures

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Cited by in corpus (2)

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