We present the results of a search for scalar and pseudoscalar particles produced in nuclear deexcitation. Measurements of the angular correlation of $e^{+}$$e^{\mathrm{-}}$ pairs emitted from excited states of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ provided sensitivity to particles with lifetimes ${10}^{\mathrm{-}19}$<τ${<10\mathrm{}}^{\mathrm{-}11}$ s within the mass range 2$m_e$<$M_X$<5 MeV. We find no evidence for such particles and set upper limits on the branching ratio to electromagnetic decay.

• Received 28 August 1987

DOI:https://doi.org/10.1103/PhysRevD.37.1134