It was an anomaly detected in a nuclear reactor storm so surprising that physicists hoped it would shed light on dark matter, one of the universe’s greatest mysteries.
However, new research has definitively ruled out that this strange measurement signaled 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—an estimated 100 trillion pass through our bodies every second.
Since neutrinos were first theorized in the 1930s, scientists have been trying to determine the properties of these shape-shifters, which are one of the most common particles in the universe.
They appear “when the nature of the nucleus of an atom has been changed,” physicist David Lhuillier of France’s Atomic Energy Commission told AFP.
This could happen when they coalesce in furious fusion at the heart of stars like our Sun or are broken apart in nuclear reactors, he said.
There are three confirmed flavors of neutrino: electron, muon, and tau.
However, physicists suspect there may be a fourth neutrino, called “sterile” because it doesn’t interact with ordinary matter at all.
In theory, it would only respond to gravity and not to the fundamental force of weak interactions, which still hold sway over other neutrinos.
The sterile neutrino has a place prepared for it in theoretical physics, “but there hasn’t been a clear demonstration that it exists yet,” he added.
The dark matter candidate
So Lhuillier and the rest of the STEREO collaboration, which brings together French and German scientists, set out to find it.
Previous measurements of nuclear reactors have found fewer neutrinos than the amount expected by theoretical models, a phenomenon called the “reactor antineutrino anomaly”.
It has been suggested that the missing neutrinos have turned into a sterile type, providing a rare chance to prove their existence.
To find out, the STEREO collaboration installed a dedicated 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 data analysis, the verdict was published in the journal. The nature Wednesday.
The anomaly “cannot be explained by sterile neutrinos,” Lhuillier said.
But that “doesn’t mean there aren’t any in the universe,” he added.
The experiment found that previous predictions of the amount of neutrinos produced were incorrect.
But it was not a total loss, providing a much clearer picture of the neutrinos emitted by nuclear reactors.
This could help not only in future research but also in the monitoring of nuclear reactors.
Meanwhile, the search for the sterile neutrino continues. Particle accelerators, which smash atoms, could provide new leads.
Despite the failure, interest may remain high because sterile neutrinos have been considered suspects for dark matter, which makes up more than a quarter of the universe but remains shrouded in mystery.
Like dark matter, the sterile neutrino does not interact with ordinary matter, making it incredibly difficult to observe.
“It would be a candidate that would explain why we see the effects of dark matter — and why we can’t see dark matter,” Lhuillier said.
David Lhuillier, STEREO neutrino spectrum of 235U fission rejects sterile neutrino hypothesis, The nature (2023). DOI: 10.1038/s41586-022-05568-2. www.nature.com/articles/s41586-022-05568-2
© 2023 AFP
Citation: Nuclear reactor experiment rules out hope for dark matter (2023, January 14) Retrieved January 15, 2023, from https://phys.org/news/2023-01-nuclear-reactor-dark.html
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