Centuries-old physics test could help detect millicharged particles

Centuries-old physics tests could aid in the detection of millicharged particles (mCPs), according to a recent study. Millicharged particles are hypothetical particles with an extremely small electric charge that are difficult to detect using conventional particle physics experiments. These particles, which are believed to make up a small fraction of dark matter, have long been predicted by theoretical physicists but remain poorly constrained due to the challenges in detecting them.

Researchers at Fermi National Accelerator Laboratory, Stanford University, and the University of Delaware have proposed that the Cavendish test, an experiment that dates back centuries and is used to measure Coulomb's law, could be adapted to search for millicharged particles. The study, published in Physical Review Letters, suggests that the Cavendish test may have greater sensitivity than particle accelerator-based experiments.

Coulomb's law is a fundamental principle that describes the electric force between charged objects. The proposed experiment involves a Faraday cage, a large conductive shell that blocks external electric fields and electromagnetic radiation. According to the researchers, if Coulomb's law and Gauss's law were exact, the Faraday cage would perfectly shield its interior, resulting in no electric field inside it.

However, the presence of millicharged particles could cause a deviation from these laws, as they could potentially penetrate the cage.

The researchers propose that the oscillating electric charges of millicharged particles could induce an oscillating electric field within the Faraday cage. This deviation from Gauss's law could provide a way to detect the presence of millicharged particles. Additionally, millicharged particles could be detected as irreducible cosmic rays produced by these particles, similar to the detection methods used in collider experiments.

The researchers believe their proposed Cavendish test could be three times more sensitive than existing or future particle accelerator-based experiments, and could potentially detect millicharged particles with charges three orders of magnitude beyond current and future accelerator-based proposals.