87: Neutrino Interaction
"Neutrino Interaction" in the Fermilab 15-foot Bubble Chamber with a heavy Neon-Hydrogen liquid mixture in April, 1976. Frequently the chamber was floods with tracks from several neutrino interactions in the same exposure. In addition to increasing the interaction rate, the heavy neon mixture allows many of the particles from neutrino interactions to be recognised by direct inspection of the track appearance: protons, charged pions and kaons produce secondary interactions; neutral pions are evidenced by their gamma rays converting to electron pairs; muons sail right through the liquid without interacting and direct electrons or positrons from the vertex are recognised by successive kinks and associated gamma ray conversions along their tracks. A major associated interest is the study of "di-lepton" events in which two muons or a muon and an electron are produced in high energy neutrino interactions.
Why bother with Neutrinos? Neutrinos are tiny -- really, really, tiny -- particles of matter. They are so small, in fact, that they pass between, and even through, atoms without interacting at all. Neutrinos are everywhere: If we start counting now, more than 1 Quintillion (that's 10^18 or one trillion billion) of them will have passed through our body by the time we finish this paragraph. Yet only one of those 1 Quintillion neutrinos will likely interact with an atom in our body. The rest will go merrily on their way! Staggering numbers of neutrinos constantly pass right through the earth and off into distant Space. Since they are so tiny, neutrinos were long thought to have no mass at all. In the last decade, however, neutrino oscillation experiments have definitively proved that neutrinos have masses, just extremely tiny ones!
The 74th HQR image in the "E8 Album" shows experiments at neutrino detectors like Super-K (Super-Kamiokande, Hida, Gifu Prefecture, Japan) and SNO (Sudbury Neutrino Observatory, Kingston, Ontario, Canada). Those experiments have established that neutrinos oscillate among various flavours, each with a different tiny mass. Neutrinos play an important role in particle physics, astrophysics and cosmology. Since neutrinos have no electric charge and have only weak interactions, they can travel much longer distances without being absorbed by matter or deflected by magnetic fields. So neutrinos can provide new information about astrophysical objects and events. Neutrino physics is one of the most remarkable -- not least because it shows up in so many different contexts. The recent discovery that neutrinos have mass is particularly significant for "vertical" questions like whether and how the forces of nature -- gravity, electromagnetism, strong and weak forces -- may be aspects of the same unified force. This is of particular interest to HQR!
Most of the neutrinos in the universe are believed to have been formed billions of years ago, during the Big Bang. Neutrinos from the Big Bang are almost stationary and there are 10 million such neutrinos in every cubic foot of space throughout the universe. These stationary neutrinos are almost impossible to detect. The more active neutrinos that we can detect are products of the nuclear reactions that fuel stars and high energy cosmic events such as the explosions of dying stars. Even with so many neutrinos around, they still don't add up to much mass. According to our present understanding, neutrinos account for at most a few percent of the total energy density of the universe, and maybe as little as a fraction of a percent. The streams of neutrinos careening away from distant collapsing stars or galaxies carry with them bits of data about the extremely high-energy events that produced them. It's a reminder that even the tiniest of particles have a fantastic tale to tell about the universe of which they are part!
The "E8 Album" photos are visual intersections of Spirituality, Science, Art and Sustainability!
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