Search for short-lived particles produced in an electron beam dump

A search for short-lived neutral particles which decay to electron-positron pairs has been carried out using a beam of 275-GeV electrons incident on an instrumental tungsten beam dump. The experiment was sensitive to particles up to 10 MeV/${\mathit{c}}^{2}$ in mass and down to 4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}16}$ sec in lifetime.