Cavendish Tests of Millicharged Particles

TL;DR

This paper shows how reinterpreting Cavendish experiments can set strong bounds on terrestrial millicharged particles and proposes enhanced setups to detect cosmic-ray-produced millicharges using existing technology.

Contribution

It demonstrates that historical Cavendish tests can be repurposed as detectors for millicharged particles and proposes new experimental configurations to improve sensitivity.

Findings

Reinterpreted past Cavendish tests as bounds on millicharged particles.

Proposed a charged shell setup to enhance detection sensitivity.

Outperforms future accelerator searches for sub-GeV millicharged particles.

Abstract

A terrestrial population of room-temperature millicharged particles can arise if they make up a dark matter subcomponent or if they are light enough to be produced in cosmic ray air showers. In a companion paper, we showed that a simple electrified shell acts as an efficient accumulator for such particles, parametrically enhancing their local density by many orders of magnitude. Here we demonstrate that Cavendish tests of Coulomb's Law, performed since the late 18th century, function as both quasistatic accumulators and detectors for this overdensity. Reinterpretations of these past Cavendish tests thus provide some of the strongest bounds on a terrestrial millicharge population. We also propose surrounding a Cavendish test with an additional charged shell, which significantly improves the sensitivity and can even enable detection of the irreducible density of millicharged particles generated from cosmic rays. Using decades-old technology, this can outperform future accelerator searches for sub-GeV masses.