Experimentally observed sharp lines in the positron-emission spectra resulting from low-energy heavy-ion collisions are interpreted in terms of the production and subsequent decay of a neutral, pseudoscalar particle. This particle has a mass of about 1.6 MeV and a lifetime of about 1.3×${10}^{\mathrm{-}13}$ sec.

• Received 1 May 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.461