Evidence for Detection of a Moving Magnetic Monopole

Abstract

A very heavy particle passed through a balloon-borne stack of Cherenkov film, emulsion, and Lexan sheets. In 33 Lexan sheets it produced tracks expected of either a nucleus with $125\lesssim Z\lesssim 137$ and $\beta \lesssim 0.92$ or a magnetic monopole with $g=137e$. Its track structure in emulsion indicated it was moving downward with $\beta ={0.5}_{-0.05\mathrm{}}^{+0.1\mathrm{}}$ and was either a nucleus with $Z\approx 80$ or a monopole with $g=137e$. These facts strongly favor identification of the particle as a magnetic monopole of strength $g=137e$ and mass $>200\mathrm{}{m}_p$.