Representatives from a team of 400 scientists from 11 countries, including Canada, revealed Friday that, for the first time, a muon neutrino was seen transformed into an electron neutrino — something never witnessed before.
The observation, announced at the European Physical Society Conference on High Energy Physics in Stockholm, allows for the possibility that neutrinos’ counterpart, anti-neutrinos, may not behave in the same way.
If that’s the case, it may help explain why the universe is made up of mostly matter and not antimatter — a phenomenon that scientists have been trying to unravel for years, said University of British Columbia physicist Hirohisa Tanaka.
Tanaka, who led a group responsible for analyzing data in the neutrino experiment known as T2K, said neutrinos come in three types and are intrinsically linked to matter. Their counterparts, anti-neutrinos, also come in the same three types, and are similarly linked to anti-matter.
When the universe was created, the Big Bang converted energy into matter and antimatter — two materials that destroy each other when they come into contact.
“In some sense, we’re asking why anything exists at all, if it wasn’t annihilated by equal quantities of matter and antimatter,” Tanaka said in an interview.
“There’s some kind of imbalance that occurred when the matter became dominant, and that is something that we can’t explain.”
Antimatter has been the fodder for many science fiction enthusiasts, used to power starships in Star Trek, and threatened to annihilate the Vatican in the popular 2000 novel Angels and Demons.
In the T2K experiment, scientists created muon neutrinos with a particle accelerator at a facility on the east coast of Japan and shot a beam of them through the ground. Three hundred kilometres at the other side of the country, the neutrinos were observed in a massive detector called the Super-Kamiokande.
The project began in 2010 and was interrupted in March 2011 when the earthquake severely damaged the accelerator. But Tanaka said through a “heroic effort,” the team managed to pull everything back together in six months.
Tanaka said scientists had always deduced muon neutrinos could transform into electron neutrinos, but this is the first time anyone has seen one disappear and the other appear.
Now scientists want to see if neutrinos’ counterparts will do the same thing, he said. If it turns out that anti-muon neutrinos do not transform into anti-electron neutrinos at the same pace, then that could point to an asymmetry between electron neutrinos and anti-electron neutrinos.
While that imbalance doesn’t necessarily solve the matter-antimatter conundrum, it’s a start, said Tanaka.
“There are a family of particles, and by studying one, you can sort of infer some of the properties of others in the family,” he said. “And it’s actually other members of the family that we believe are responsible for this imbalance in the universe.”
Tanaka said to see whether an imbalance exists between the way muon neutrinos and anti-muon neutrinos transform, an enormous cavern would need to be dug out of a mountain to fit in a much larger detector — a project that is currently in the proposal stage.
“By studying these elementary particles, we’re sort of looking at the universe near the time of the Big Bang,” he said.
“It gives us a glimpse into what might have happened, what particles where doing, and explaining how the universe started from the Big Bang to where we are now, with galaxies, and molecules and…people.”