Paul Scherrer Institute neutron experiment rules out mirror‑neutron switching

Researchers at the Paul Scherrer Institute (PSI) conducted a high‑precision test with about 25 billion ultracold neutrons, varying magnetic fields to search for oscillations of neutrons into hypothetical mirror‑neutron states. The study found no evidence of such transformations, excluding 99.98 % of the previously considered parameter space and casting doubt on the mirror‑matter explanation for dark matter.

Geza Zsigmond of PSI’s Center for Neutron and Muon Sciences explained that mirror particles would only interact via gravity, while Bernhard Lauss noted, “There is no way of proving the existence of mirror particles using gravitational interaction alone.” The results do not completely rule out all mirror‑matter models but substantially limit one of their key predictions.