In its common form, double beta decay is a process in which a nucleus decays into a different nucleus and emits two electrons and two antineutrinos. Scientists are looking for lepton number violation in a process called double beta decay, says SLAC theorist Alexander Friedland, who specializes in the study of neutrinos. And neutrino interactions could be the place to find that loophole. Somehow, that's not what happened.įinding out that lepton number is not conserved would open up a loophole that would allow for the current imbalance between matter and antimatter. The two types of particles should have interacted, gradually canceling one another until nothing but energy was left behind. Scientists think that, just after the big bang, the universe should have contained equal amounts of matter and antimatter. Scientists consider it a fundamental law of nature that lepton number is conserved, meaning that the number of leptons and anti-leptons involved in an interaction should remain the same before and after the interaction occurs. The key to finding this evidence is something called lepton number conservation. Since then, experiments have cropped up across Asia, Europe and North America searching for hints that the neutrino is its own antiparticle. Whether neutrino masses were zero remained a mystery until 1998, when the Super-Kamiokande and SNO experiments found they do indeed have very small masses - an achievement recognized with the 2015 Nobel Prize for Physics. The Majorana equation described neutrinos that, if they happened to have mass after all, could turn into antineutrinos and then back into neutrinos again. In 1937, Italian physicist Ettore Majorana debuted another theory: Neutrinos and antineutrinos are actually the same thing. A particle can have either a right-handed or left-handed chirality.ĭirac's equation allowed for neutrinos and antineutrinos to be different particles, and, as a result, four types of neutrino were possible: neutrinos with left- and right-handed chirality and antineutrinos with left- and right-handed chirality.īut if the neutrinos had no mass, as scientists thought at the time, only left-handed neutrinos and right-handed antineutrinos needed to exist. He called it the positron - a particle like an electron but with a positive charge.ĭirac predicted that, in addition to having opposite charges, antimatter partners should have another opposite feature called chirality, which represents one of the inherent quantum properties a particle has. Physicist Carl Anderson discovered the antimatter partner of the electron that Dirac foresaw in 1932. "Antiparticles are a consequence of his equation." "When Dirac wrote down his equation, that's when he learned antiparticles exist," says André de Gouvêa, a theoretical physicist and professor at Northwestern University. But his calculations resulted in a strange requirement: that electrons sometimes have negative energy. His work sought to explain what happened when electrons moved at close to the speed of light. The idea of the antiparticle came about in 1928 when British physicist Paul Dirac developed what became known as the Dirac equation. But if scientists discover neutrinos are their own antiparticles, it could be a clue as to where they get their tiny masses - and whether they played a part in the existence of our matter-dominated universe. Gluons and even Higgs bosons are thought to be their own antiparticles. Judging by the particles released when a neutrino interacts with other matter, scientists can tell when they've caught a neutrino versus an antineutrino.īut certain characteristics of neutrinos and antineutrinos make scientists wonder: Are they one and the same? Are neutrinos their own antiparticles? This seems to be true of neutrinos, tiny particles that are constantly streaming through us.
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