Implications of a new particle from the HyperCP data on Σ+→pμ+μ-

The HyperCP Collaboration has recently reported the observation of three events for the decay Σ⁺→pμ⁺μ^- with an invariant mass m_μ+μ- for the muon-antimuon pair of ∼214 MeV. They suggest that a new particle state X may be needed to explain the observed m_μ+μ- distribution. Motivated by this result, we study the properties of such a hypothetical particle. We first use K ⁺→π⁺μ⁺μ^- data to conclude that X cannot be a scalar or vector particle. We then collect existing constraints on a pseudoscalar or axial-vector X and find that these possibilities are still allowed as explanations for the HyperCP data. Finally we assume that the HyperCP data is indeed explained by a new pseudoscalar or axial-vector particle and use this to predict enhanced rates for K _L→ππX→ππμ⁺μ^- and Ω^-→Ξ^-X→Ξ^-μ ⁺μ^-.