Implications of a new particle from the HyperCP data on Σ^+ \to p μ^+ μ^-

The HyperCP collaboration has recently reported the observation of three events for the decay Σ^+ \to p mu^+ mu^- with an invariant mass m_{μ^+μ^-} for a muon and an anti-muon pair of \sim 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^+ \to pi^+ μ^+μ^- data to conclude that X cannot be a scalar or a vector particle. We then collect existing constraints on a pseudo-scalar 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 pseudo-scalar or axial vector particle and use this to predict enhanced rates for K_L \to π^+π^- X \to π^+π^-μ^+μ^- and Ω^- to Ξ^- X \to Ξ^- μ^+μ^-.

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