Search for New Massive Long-Lived Neutral Particles

Abstract

We have carried out a search for neutral hadrons with masses ≳2 GeV/${\mathit{c}}^2$ and proper lifetimes ≳${10}^{-7\mathrm{}}$ sec in the $M4\mathrm{}$ neutral beam at Fermilab. The particle masses were determined from their flight time and kinetic energy. Our upper limits for the production cross section of such particles are ${10}^{-1\mathrm{}}$ to ${10}^{-3\mathrm{}}$ times those for the production of $\psi \text{'}\mathrm{s}$ by protons for comparable kinematic conditions. This is the most sensitive search to date for quasistable neutral particles with masses ≳2 GeV/${\mathit{c}}^2$.