Experimental Upper Limit on the Magnetic Monopole Moment of Electrons, Protons, and Neutrons, Utilizing a Superconducting Quantum Interferometer

Abstract

A superconducting quantum interferometer (magnetic flux sensitivity \ensuremath{\sim}${10}^{\ensuremath{-}17}$ Wb) is shown to be capable of directly detecting magnetic charge, in particular Dirac's quantized magnetic monopoles ($\mathrm{magnetic}\mathrm{flux}=\frac{h}{e}=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ Wb). In samples free of Dirac monopoles, divB was determined to be less than 1.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ Wb/kg, while the magnetic charge of the neutron and of the proton (relative to the electron) were found to be less than ${10}^{\ensuremath{-}26}$ Dirac monopole per nucleon. The magnetic charge of the electron itself was measured to be less than 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ Dirac monopole.