Testing the neutrality of matter by acoustic means in a spherical resonator

TL;DR

This paper reports a new acoustic method using a spherical resonator filled with SF6 to test the neutrality of matter, achieving the most stringent limit to date on charge differences between particles.

Contribution

It introduces a novel acoustic measurement technique with a spherical capacitor to set new limits on matter's neutrality, improving upon previous methods.

Findings

Established a limit of ε_{p-e} ≲ 1×10^{-21} for charge difference

Calibrated apparatus using electric polarizability measurements

Critically reviewed and improved upon previous measurements

Abstract

New measurements to test the neutrality of matter by acoustic means are reported. The apparatus is based on a spherical capacitor filled with gaseous SF$_6$ excited by an oscillating electric field. The apparatus has been calibrated measuring the electric polarizability. Assuming charge conservation in the $\beta$ decay of the neutron, the experiment gives a limit of $\epsilon_\text{p-e}\lesssim1\cdot10^{-21}$ 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.