Is the smallest, lightest, most ghostly particle about to upend our understanding of the universe? Recently, the ephemeral neutrino has begun to give up some of its secrets. Beginning in 1998 the neutrino experiments at Super-Kamiokande and Sudbury Neutrino Observatory showed for the first time that neutrinos oscillate with one of three flavors. In 2015, two physicists were awarded the Nobel prize for this discovery, which also proved that neutrinos must have mass. More recently, a small anomaly at the Super-Kamiokande detector has surfaced, which, is hoped, could shed light on why the universe is constructed primarily from matter and not anti-matter.
The anomaly, detected by the T2K experiment, is not yet pronounced enough to be sure of, but it and the findings of two related experiments “are all pointing in the same direction,” said Hirohisa Tanaka of the University of Toronto, a member of the T2K team who presented the result to a packed audience in London earlier this month.
“A full proof will take more time,” said Werner Rodejohann, a neutrino specialist at the Max Planck Institute for Nuclear Physics in Heidelberg who was not involved in the experiments, “but my and many others’ feeling is that there is something real here.”
The long-standing puzzle to be solved is why we and everything we see is matter-made. More to the point, why does anything — matter or antimatter — exist at all? The reigning laws of particle physics, known as the Standard Model, treat matter and antimatter nearly equivalently, respecting (with one known exception) so-called charge-parity, or “CP,” symmetry: For every particle decay that produces, say, a negatively charged electron, the mirror-image decay yielding a positively charged antielectron occurs at the same rate. But this cannot be the whole story. If equal amounts of matter and antimatter were produced during the Big Bang, equal amounts should have existed shortly thereafter. And since matter and antimatter annihilate upon contact, such a situation would have led to the wholesale destruction of both, resulting in an empty cosmos.
Somehow, significantly more matter than antimatter must have been created, such that a matter surplus survived the annihilation and now holds sway. The question is, what CP-violating process beyond the Standard Model favored the production of matter over antimatter?
Many physicists suspect that the answer lies with neutrinos — ultra-elusive, omnipresent particles that pass unfelt through your body by the trillions each second.
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