PARTICLE // Tau, Neutrino

A tau neutrino is an elementary particle with zero charge, 1/2 spin, and an incredibly low mass (even by particle standards), less than 2.14 x 10^-34 kg!

Tau neutrinos are most commonly produced when particles called D_s mesons decay into tau particles and tau neutrinos. They are among the least studied and most mysterious particles in the standard model, since on top of the usual difficulties with studying neutrinos (which interact with other particles so rarely that hundreds of trillions can pass through the Earth each second without interacting), tau neutrinos are both difficult to produce in the lab and difficult to distinguish from electron neutrinos using our current detectors.

In fact, despite their existence being theorized since the discovery of the tau lepton in 1975, tau neutrinos were not actually observed until the year 2000, making them the second-most-recently observed particle in the standard model (right behind the famous higgs boson, which was first observed in 2012).

Like all neutrinos, muon neutrinos can also spontaneously oscillate into a different “flavor” while in flight, becoming an electron neutrino or muon neutrino. (Though in reality, they are actually a quantum mechanical mix of all three flavor states, like how Schrödinger’s famous cat is a mix of alive and dead.)

Want to learn more?

For more about these incredible particles, check out Fermilab’s all things neutrinos page!