Here’s part II of the explanation of my PhD thesis. Part I is here.
Remember from part I that there are 3 charged leptons (the electron’s extended family): the electron, muon, and tau. There are also three neutrinos, each associated with one of those charged leptons: the electron neutrino, the muon neutrino, and the tau neutrino.
Here’s the whole gang in stuffed-animal form:
What hams they are! Look at those mugs! Say cheese, little leptons! (If you want your own stuffed lepton, you can find them here.)
So why do we name the neutrinos this way? It’s because each neutrino is always produced in association with the charged lepton in its name.
A good example is beta decay. You might remember this from chemistry—it’s one of the main kinds of radioactivity. In this type of radioactive decay, an unstable atom changes from one element to another, and an electron is emitted. But a neutrino is also emitted at the same time. You didn’t know that part about the neutrino, huh? Well, at first, physicists didn’t know about the neutrino either, and it caused a huge scientific hullabaloo. But radioactive man was unfazed!
Ahem. Anyway, back to beta decay. Since the neutrino we get from beta decay is produced in conjunction with an electron, that means it’s an electron neutrino. (OK, actually it’s an electron antineutrino, the antimatter version of the particle, but that’s not super-important for our purposes.) And when an electron neutrino interacts and creates a charged lepton, it will always always always produce an electron. It will never produce a muon or a tau. That’s how we know these are three different particles.
OK. We’re now finally ready to tackle the subject of my thesis: neutrino oscillations. Phew. Stay with me!