Quest for Faster-Than-Light Particles

An experimental search for the existence of particles that propagate with velocities that are always greater than the velocity of light in a vacuum has been performed. Subject to some assumptions regarding the behavior of such particles, it is found that the photoproduction cross section for such particles in lead is less than 3×${10}^{-30\mathrm{}}$ ${\mathrm{cm}}^2$. This upper limit does not depend strongly on the "rest mass" of the particles and is approximately the same for faster-than-light particles of any "rest mass." This search was sensitive to particles having charges between 0.1 and 2 electron charges.