Sudbury Neutrino Observatory
Other Scottish Country Dances for this Day
Today's Musings, History & Folklore
"I have done a terrible thing: I have postulated a particle that cannot be detected."
~ Wolfgang Pauli (1900-1958)
Physicists nowadays spend much of there time hunting the invisible and undetectable! In the case of the neutrino, however, much is now known. There are three types of neutrinos, tiny particles once thought to be massless: electron neutrino, muon neutrino, and tau neutrino, Every day, the solar neutrino flux for us on Earth is about 65 billion neutrinos, passing through just one square centimeter of area on earth, every second. That means over the course of your lifetime, about 10^23 neutrinos will stream through your body – that’s almost a trillion trillions! ⚛️⚛️⚛️
Reel of the Neutrino
The Sanford Underground Laboratory (SURF) in Lead, South Dakota, celebrates Neutrino Day, a science festival focussing on the engineering and science behind the Deep Underground Neutrino Experiment (DUNE), one of several labs throughout the world that focus on this elementary particle.
A neutrino(denoted by the Greek letter ν) is a fermion (an elementary particle with half-integer spin) that interacts only via the weak subatomic force and gravity. The mass of the neutrino is much smaller than that of the other known elementary particles.
In 2015, the Nobel Prize in Physics was awarded to Takaaki Kajita in Japan and Arthur B. McDonald in Canada, for their key contributions to the experiments which demonstrated that neutrinos change identities.
From the 2015 press release:
The Nobel Prize in Physics 2015 recognises Takaaki Kajita in Japan and Arthur B. McDonald in Canada, for their key contributions to the experiments which demonstrated that neutrinos change identities. This metamorphosis requires that neutrinos have mass. The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe.
Around the turn of the millennium, Takaaki Kajita presented the discovery that neutrinos from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Japan.
Meanwhile, the research group in Canada led by Arthur B. McDonald could demonstrate that the neutrinos from the Sun were not disappearing on their way to Earth. Instead they were captured with a different identity when arriving to the Sudbury Neutrino Observatory.
A neutrino puzzle that physicists had wrestled with for decades had been resolved. Compared to theoretical calculations of the number of neutrinos, up to two thirds of the neutrinos were missing in measurements performed on Earth. Now, the two experiments discovered that the neutrinos had changed identities.
The discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered massless, must have some mass, however small.
For particle physics this was a historic discovery. Its Standard Model of the innermost workings of matter had been incredibly successful, having resisted all experimental challenges for more than twenty years. However, as it requires neutrinos to be massless, the new observations had clearly showed that the Standard Model cannot be the complete theory of the fundamental constituents of the universe.
For more on the hunt for the neutrino, click the colliding neutrinos.