The search for s-channel production of light neutral particles coupled to ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ has been extended by more than 3 orders of magnitude in lifetime beyond the region which is accessible to elastic ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ scattering. The whole mass range 1500≲${\mathit{M}}_{\mathit{X}}^0$≲1860 keV/${\mathit{c}}^2$ suggested by the observation of anomalous ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ pairs in heavy-ion collisions has been investigated. These measurements find no evidence for ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ states within lifetime ranges (90% C.L.) of 1.4×${10}^{\mathrm{-}12}$≲τ≲4×${10}^{\mathrm{-}10}$ sec (J=0) and 1.4×${10}^{\mathrm{-}12}$≲τ≲6×${10}^{\mathrm{-}10}$ sec (J=1), assuming that the state does not break up by interacting within the target.

• Received 3 March 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.1733