Radiative quarkonium decays and the NMSSM Higgs interpretation of the HyperCP Sigma+ --> p mu+mu- events

We study the potential of radiative decays of the Upsilon(1S) and of the phi mesons to search for a light pseudoscalar Higgs boson, proposed as a possible interpretation of Sigma+ --> p mu+mu- events observed by the HyperCP collaboration at Fermilab. We conclude that the detection of this signal should certainly be possible with the current CLEO Upsilon(1S) data, and is within the reach of KLOE in at least part of the range of couplings suggested by the HyperCP findings.