Search for Free Fractional Electric Charge Elementary Particles

TL;DR

This study conducted a highly sensitive search for free fractional electric charge particles in bulk matter using an improved Millikan oil drop method, finding no evidence and setting stringent upper limits on their concentration.

Contribution

It presents the largest mass sample and an advanced automated technique to search for fractional charge particles, improving sensitivity over previous experiments.

Findings

No fractional charge particles detected.

Upper limit of 4.71×10⁻²² particles per nucleon.

Enhanced automated Millikan oil drop technique.

Abstract

We have carried out a direct search in bulk matter for free fractional electric charge elementary particles using the largest mass single sample ever studied - about 17.4 mg of silicone oil. The search used an improved and highly automated Millikan oil drop technique. No evidence for fractional charge particles was found. The concentration of particles with fractional charge more than 0.16e (e being the magnitude of the electron charge) from the nearest integer charge is less than $4.71\times10^{-22}$ particles per nucleon with 95% confidence.