Does the HyperCP Evidence for the Decay ${\Sigma }^{+}\to p{\mu }^{+}{\mu }^{-}$ Indicate a Light Pseudoscalar Higgs Boson?

The HyperCP Collaboration has observed three events for the decay ${\Sigma }^{+}\to p{\mu }^{+}{\mu }^{-}$ which may be interpreted as a new particle of mass 214.3 MeV. However, existing data from kaon and $B$-meson decays provide stringent constraints on the construction of models that support this interpretation. In this Letter we show that the “HyperCP particle” can be identified with the light pseudoscalar Higgs boson in the next-to-minimal supersymmetric standard model, the $A_1^0$. In this model there are regions of parameter space where the $A_1^0$ can satisfy all the existing constraints from kaon and $B$-meson decays and mediate ${\Sigma }^{+}\to p{\mu }^{+}{\mu }^{-}$ at a level consistent with the HyperCP observation.

Figure 1

Branching ratios of ${\Sigma }^{+}\to p{A}_1^0$ (solid curves), $K^{+}\to {\pi }^{+}{A}_1^0$ (dotted curves), and $K_S\to {\pi }^0{A}_1^0$ (dashed curves) as functions of $g_{\mathcal{A}}$ for $l_d=0.35$. The horizontal lines indicate the bounds from the HyperCP result and the kaon bounds from Eq. (1). The allowed range in this case is $0.38\lesssim {10}^7{g}_{\mathcal{A}}\lesssim 0.43$.

Figure 2

Parameter space for $m_{\tilde{u}}-m_{\tilde{c}}$ and $m_2/(-\lambda x)$ where $A_1^0$ can explain the HyperCP events (gray regions) and simultaneously satisfy the kaon bounds (black regions), with the input described in the text.