How neutrinos offer clues to the matter-antimatter puzzle

If you go to the zoo, you will find a dizzying variety of animals — some familiar and some completely strange. The same is true of researchers trying to study matter’s smallest components. While the proton, neutron, and electron are familiar, the subatomic zoo is inhabited by many entirely unfamiliar particles. In a recent result announced at a conference in Italy by researchers at the Fermi National Accelerator Laboratory, the properties of a ghostly particle called a neutrino are coming into focus.

Neutrinos are the wraiths of the subatomic world, able to pass through the entire Earth with just a small chance of interacting. They are most commonly produced in nuclear reactions, which means that each of us encounters a steady rain of neutrinos coming from the biggest nuclear reactor: the Sun. Every second, something like 100 billion neutrinos pass through you. That sounds scary, but the neutrino’s low probability of interacting with matter means that during your entire life perhaps only one of them will stop inside your body.

Scientists know of three types of neutrinos, each associated with a “cousin” charged particle, the most familiar of which is called the electron. The other particles, called the muon and tau lepton are essentially unstable and heavy electrons that decay in a fraction of a second. The three different types of neutrinos are called the electron neutrino, muon neutrino, and tau neutrino.

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