Search for Heavy Magnetic Monopoles

The discovery of an apparent breakdown in time-reversal invariance in ${K_2}^0$ decays demands further investigation into the symmetry properties of the fundamental interactions. Since a simple model of electric charge and magnetic poles leads to an electrodynamics which is not time-reversal invariant, it appeared essential to extend previous investigations concerning the possible existence of magnetic monopoles to regions of higher monopole mass and lower production cross section. An experiment was designed to detect monopoles produced in the earth's atmosphere by the primary cosmic radiation following a method introduced by Malkus. A solenoid with a magnetic moment of 3×${10}^5$ A ${\mathrm{m}}^2$ was used to collect monopoles moving along the earth's lines of magnetic flux and to accelerate them through scintillation counters, a spark chamber, and into emulsions. The negative results of the search show that the monopole flux at the surface of the earth is less than ${10}^6$/${\mathrm{cm}}^2$ year. Using for the sake of comparison, a simple model of monopole production such that the cross section is constant above threshold, this result shows that the cross section for the production of monopoles by nucleon-nucleon interactions is less than ${10}^{-6\mathrm{}}{\left(\frac{\hslash }{\mathrm{Mc}}\right)}^2$ for a monopole mass $M$ of 15 BeV/${\mathit{c}}^2$. The limit on the production of monopoles by photonucleon interactions is about ${10}^3$ times higher. In both cases the cross-section limit varies with monopole mass approximately as $M^{3.4}$.