摘要
We investigate various search strategies for light vector boson X in O(10) MeV mass range using J/Ψ associated channels at BESIII and Belle II: (i) J/Ψ → η c X with 10 10 J/Ψs at BESIII, (ii) J/Ψ(η c + X) + ℓ ℓ ¯ production at Belle II, and (iii) J/Ψ + X with the displaced vertex in X → e + e − decay are analyzed and the future sensitivities at Belle II with 50 ab −1 luminosity are comprehensively studied. By requiring the displaced vertex to be within the beam pipe, the third method results in nearly background-free analysis, and the vector boson-electron coupling and the vector boson mass can be probed in the unprecedented range, 10 −4 ≤ |ε e | ≤ 10 −3 and 9 MeV ≤ m X ≤ 100MeV with 50 ab −1 at Belle II. This covers the favored signal region of 8 Be * anomaly recently reported by Atomki experiment with m X ≃ 17 MeV.