Constraints on the new particle in Σ+→pμ+μ−

The HyperCP Collaboration has presented the branching ratio of Σ+→pμ+μ− to be (8.6−5.4+6.6±5.5)×10−8 and suggested a new boson P0 with a mass of 214.3±0.5MeV to induce the flavor changing transition of s→dμ+μ−. We demonstrate that to explain the data, the new particle cannot be a scalar but pseudoscalar based on the direct constraints from K+→π+μ+μ− and KL→μ+μ−, respectively. Moreover, we determine that the decay width of the pseudoscalar should be in the range of 10−7MeV with the lifetime of 10−14 s.