How the SuperNEMO experiment could help solve the mystery of the origin of matter in the universe

June 28, 2020

 The SuperNEMO detector, around six metres long, four metres high and three metres wide, sits in a tightly controlled clean room to protect it from contamination by the minute amounts of natural radioactivity present in dirt and dust is Europe’s deepest underground laboratory. The job of SuperNEMO is to watch over seven kilograms of selenium and search for one of the rarest forms of radioactivity there is: double-beta decay. Double-beta decay is a process by which two neutrons in a selenium nucleus simultaneously decay into protons, while emitting two electrons and two particles called antineutrinos.  

The kinds of neutrinos and antineutrinos SuperNEMO is looking at are of the so-called electron type. When the neutrinos interact with matter they produce negatively charged electrons, but when the antineutrinos interact with matter they produce positively charged positrons, the electron’s antiparticle. But before the neutrino or antineutrino interacts, how does it know which one it is? This profound question led to consider whether the neutrino and the antineutrino could in fact be exactly the same particle, just spinning in opposite directions.


If the antineutrinos created in the double-beta decay that SuperNEMO is looking for have the ability to behave like neutrinos, then just occasionally one of them might do that. That would mean you had an antineutrino and a neutrino next to each other – which would mean they could annihilate each other. Should that happen, the two electrons produced in the double-beta decay would get an extra kick of energy from the annihilation – and that is what SuperNEMO is looking for: a tiny kick of energy that would require us to rethink how matter and antimatter are related.

If our two antineutrinos annihilate (because one of them behaved like a neutrino at the time), then the double-beta decay would produce two matter-like electrons and no antimatter to balance them out. That’s not allowed in the Standard Model, which requires that matter and antimatter are always produced in equal amounts.

This brings us to one of the most profound questions of physics: why is there more matter than antimatter in the universe? You might think we already know the answer to that: the Big Bang produced all the matter. Well, yes it did, but it should have also produced an equal amount of antimatter. So why did all the matter and antimatter not annihilate each other to leave nothing but a sea of light? The SuperNEMO can therefore put great insight into the origins of matter.


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