Search for Superheavy Monopoles in 65 kg of Iron Magnetic Sand with a SQUID Fluxmeter

Abstract

A search was carried out for magnetically trapped monopoles in 65 kg of iron sand with a SQUID-search coil 80 mm in diameter, by heating the sample above its Curie point. We have found no candidate event compatible with the passage of a single Dirac charge. An upper limit of 1.5×10⁻⁵ monopoles/g is set for the density of monopoles heavier than 2.5×10¹⁵ GeV/c² in the iron sand of (6∼25)×10⁶ years old. We can estimate the flux of cosmic monopole as less than 1.3×10⁻¹¹ cm⁻²sec⁻¹sr⁻¹ according to the age and the density of the sample examined.