Search for an Electron-Proton Charge Inequality by Charge Measurements on an Isolated Macroscopic Body

A new method is reported for testing the electrical neutrality of matter containing an equal number of protons and electrons. A small iron spheroid was magnetically suspended in a uniform, horizontal electric field in such a manner that it was possible to measure electric deflecting forces small enough to detect 0.03 proton charge on the spheroid. An upper limit to the charge difference between the proton and electron, defined by f=1+(electroncharge)/(protoncharge), was found to be |f|≤0.8×10^-19. It was necessary to assume: (neutron charge) = (electron charge) + (proton charge). Values of f in the range 0.8×10^-19<|f|<2.8×10^-19 were excluded, and the probability that |f|>0.8×10^-19 is not greater than 0.2. A by-product of the measurements was the finding that the iron spheroids contained less than 1 quark in 2.5×{}10¹⁸ nucleons. The measurements also permitted an estimate that the absolute electric charge on 2-eV photons is less than 10^-16 proton charge.