They come in three flavors and can transform among these different types as they travel. They pass through most matter undetected and uninterrupted. Tens of trillions of them are passing through your body in the time it takes to read this sentence. But don’t worry – they are harmless. They are produced by the sun, within the Earth, at nuclear reactors, by exploding stars, and by cosmic rays interacting with Earth’s atmosphere, among other sources.
While many experiments, past and present, have taught us much about them, they remain the source of many unanswered questions and unsolved mysteries in science. A string of ambitious new experiments seek to fill in some of the most important gaps in our knowledge.
Each of their three types also has an antimatter counterpart, and it’s not yet clear whether these counterparts are essentially the same as their normal forms – the answer to this could help explain whether they played a substantial role in the abundance of matter vs. antimatter in the universe.
We know they have three different masses, too, but we aren’t yet sure which of these three is the lightest or heaviest.
They were discovered in 1956, and they were proposed to exist 90 years ago, on Dec. 4, 1930.
“They,” as it happens, are subatomic particles called neutrinos, and the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has a long history of participating in neutrino experiments and discoveries in locations ranging from a site 1.3 miles deep at a nickel mine in Ontario, Canada, to an underground research site near a nuclear power complex northeast of Hong Kong, and a neutrino observatory buried in ice near the South Pole.
In a Dec. 4, 1930, letter proposing the existence of these particles, Austrian physicist Wolfgang Pauli said they were an “almost improbable” and “desperate remedy” to preserve a fundamental physics law while explaining an apparent energy deficit in nuclear decay processes occurring in some atomic nuclei. Pauli had first referred to the particles as “neutrons,” though physicist Enrico Fermi in 1934 renamed these hypothesized particles “neutrinos” – Italian for “little neutral ones.”
To celebrate how far neutrino science has come in the 90 years since Pauli made his particle prediction, Berkeley Lab has prepared this list highlighting some of the landmark neutrino experiments and results its scientists have contributed to.