Why cant we tell the mass of electron neutrinos, mu neutrinos, and tau

[Waveparticle]

Why can't we tell the mass of electron neutrinos, mu neutrinos, and tau neutrinos?

 

[JustinLevy]

First, neutrinos rarely interact, so scientists have to go to some pretty big extremes to observe them compared to electrons, muons, etc. Secondly, neutrinos are so light that mc^2 << KineticEnergy for essentially all lab experiments that measure them. So the mass is essentially "negligible". If it wasn't for flavor oscillation, we mave have very well never detected that they even have a mass. Unfortunately, this phenomenom is only sensitive to the difference is masses between the neutrinos ... so we can't use it to measure their masses absolutely.

I think there are some experiments (can someone correct me?) planned that will be able to fix the neutrino mass scale. With enough statistics, hopefully they will succeed.

 

[Parlyne]

In fact neutrino oscillations are only sensitive to the difference of the squares of the masses.

Also, even once we've been able to measure neutrino masses individually, we still won't be able to say anything about the masses of the electron, muon, and tau neutrinos because, those states do not have definite mass. The whole point with neutrino oscillations is that one of these state can turn into another specifically because they aren't the states of definite mass, but, rather, are superpositions of the mass states.