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

The HyperCP collaboration has recently reported the observation of three events for the decay \Sigma^+ \to p mu^+ mu^- with an invariant mass m_{\mu^+\mu^-} 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_{\mu^+\mu^_} distribution. Motivated by this result, we study the properties of such a hypothetical particle. We first use K^+ \to pi^+ \mu^+\mu^- 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 \pi^+\pi^- X \to \pi^+\pi^-\mu^+\mu^- and \Omega^- to \Xi^- X \to \Xi^- \mu^+\mu^-.