An anomaly detected in the storm of a nuclear reactor was so confusing that physicists hoped it would shed light on one of the universe’s greatest mysteries, dark matter.
But new research has firmly denied that this strange measurement indicates 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 – it’s estimated that about 100 trillion pass through our bodies every second.
Since neutrinos were first theorized in 1930, scientists have been trying to determine the properties of these shapeshifters, one of the most common particles in the universe.
They occur “when the nature of an atom’s nucleus changes,” physicist David Lhuillier of the French Atomic Energy Commission told AFP.
This can happen when they come together in violent fusion at the heart of stars like our Sun, or when they break apart in nuclear reactors, he said.
There are three confirmed variants of the neutrino: electron, muon, and tau.
But physicists suspect there may be a fourth neutrino, dubbed “sterile” because it never interacts with ordinary matter.
Theoretically, it would only respond to gravity, not the fundamental force of weak interactions that still have an effect on other neutrinos.
“The vicious neutrino has a ready place in theoretical physics, but there is no clear proof that it exists yet,” he added.
– Dark matter candidate –
So Lhuillier and the rest of the STEREO collaboration that brought together French and German scientists set out to find it.
Previous nuclear reactor measurements had found fewer neutrinos than theoretical models expected, a phenomenon called the “reactor antineutrino anomaly.”
It has been suggested that the missing neutrinos have mutated into the vicious species, offering a rare chance to prove their existence.
To find out, the STEREO collaboration placed a special detector a few meters 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 of analyzing the data, the decision was published Wednesday in the journal Nature.
Lhuillier said the anomaly “cannot be explained by sterile neutrinos.”
But that “doesn’t mean it doesn’t exist at all in the universe,” he added.
The experiment found that previous estimates of the amount of neutrinos produced were wrong.
But it wasn’t a complete loss, offering a much clearer picture of the neutrinos emitted by nuclear reactors.
This could aid not only future research but also monitoring nuclear reactors.
Meanwhile, the search for sterile neutrinos continues. Particle accelerators that split atoms may offer new clues.
Despite the setback, interest may remain high because vicious neutrinos are seen as a suspect for dark matter, which makes up more than a quarter of the universe but remains a mystery.
Like dark matter, the sterile neutrino does not interact with ordinary matter, making it incredibly difficult to observe.
“It would be a candidate to explain why we see effects of dark matter and why we can’t see dark matter,” Lhuillier said.