Search for new, long-lived, neutral particles

We have searched for new particles of charge zero, a mass between 1.5 and 7.5 GeV/$c^2$, and lifetimes between ${10}^{\mathrm{-}8}$ and 2×${10}^{\mathrm{-}6}$ sec, produced by 400-GeV/c protons striking a beryllium target. The experiment looked for structure in the transverse-momentum spectrum of charged particles arising from decays in the Fermilab M3 neutral beam. No new particles were found. We place upper limits on the production cross section of any such particle.