Neutrinos

[wam_mi]

Hi everyone,

I have a few queries about neutrinos. I have recently read that there are 3 generations of neutrinos, namely the electron neutrino, the muon neutrino and the tau neutrino.

Q1: Why are they all massive particles and is it true that it is more favourable to go from muon neutrino to electron neutrino and why is that? Is it something to do with stability or decay? Any experimental evidence?

Q2: As for experimental evidence, do we need to have a lot of energy/power to detect these massive weakly interacting particles? Why is it that they only undergo weak interactions?

Q3: Follow up from Q1, is it possible if we can make the decay from electron neutrino to muon neutrino just as favourable as the process from muon neutrino to electron neutrino? If yes, how do we achieve that?


Thanks guys!

[fatra2]

Q1: From my understanding, it is only experimental evidence that shows the favourable mutation to electronic neutrino.

Q2: The neutrino are electrically neutral (do not interact with the elctromagnetic force), with incredibly little mass (gravity does affect them). Furthermore, they are leptons (strong nuclear interaction of a nucleus does not work). Therefore, you need a direct hit with a nucleus to be able to detect a neutrino.

Cheers

[jtbell]

Why are they all massive particles

Why shouldn't they be? :smile: Before there was evidence that they have mass, it was a puzzle why they were apparently massless! It's still something of a puzzle why the masses are so small.

do we need to have a lot of energy/power to detect these massive weakly interacting particles?

The interaction cross section increases with energy, that is, higher-energy neutrinos are more likely to interact with a "target" than low-energy ones. That's why a lot of neutrino research has been done at accelerators that can produce beams of high-energy neutrinos (10's or 100's of GeV rather than the few hundred MeV that you get e.g. from solar neutrinos).

Why is it that they only undergo weak interactions?

That's just the way they are. The standard model defines them as part of the weak-interaction sector. They're presumably also affected by gravity, but I don't think that's been studied experimentally at all, except maybe indirectly via cosmological data and theory.

[nicksauce]

Why is it that they only undergo weak interactions?

Well, they're leptons, so they don't interact strongly, and they're uncharged so they don't interact electromagnetically. Weak is all that's left.