New measurements to test the neutrality of matter by acoustic means are reported. The apparatus is based on a spherical capacitor filled with gaseous SF6 excited by an oscillating electric field. The apparatus has been calibrated measuring the electric polarizability. Assuming charge conservation in the β decay of the neutron, the experiment gives a limit of ϵp-e≲1⋅10−21 for the electron-proton charge difference, the same limit holding for the charge of the neutron. Previous measurements are critically reviewed and found incorrect: the present result is the best limit obtained with this technique.
@article{arxiv.1102.2766,
title = {Testing the neutrality of matter by acoustic means in a spherical resonator},
author = {G. Bressi and G. Carugno and F. Della Valle and G. Galeazzi and G. Ruoso and G. Sartori},
journal= {arXiv preprint arXiv:1102.2766},
year = {2015}
}