PARIS: It was an anomaly detected in the storm of a nuclear reactor so puzzling that physicists hoped it would shine a light on dark matter, one of the universe’s greatest mysteries.

But new research has definitively ruled out that this strange measurement signalled the existence of a “sterile neutrino”, a hypothetical particle that has long eluded scientists.

Neutrinos are sometimes called “ghost particles” because they barely interact with other matter.

They appear “when the nature of the nucleus of an atom has been changed”, physicist David Lhuillier of France’s Atomic Energy Commission, said.

There are three confirmed flavours of neutrino: electron, muon and tau. But physicists suspect there could be a fourth neutrino, dubbed “sterile” because it does not interact with ordinary matter at all.

The sterile neutrino has a place ready for it in physics, “but there has not yet been a clear demonstration that is exists”, the physicist added.

It was suggested that the missing neutrinos had changed into the sterile kind, offering a rare chance to prove their existence.

To find out, the STEREO collaboration installed a dedicated detector a few metres away from a nuclear reactor used for research at the Laue-Langevin institute in Grenoble, France.

After four years of observing more than 100,000 neutrinos and two years analysing the data, the verdict was published in the journal Nature on Wednesday.

The anomaly “cannot be explained by sterile neutrinos,” Lhuillier said.

Published in Dawn, January 13th, 2023