Question

At the KIT they have been measuring the mass of the electron neutrino with a huge spectrometer (i.e. they make an enormous effort) and already published limits on the highest possible electron neutrino mass (it is already less than 1

eV). How is this compatible with neutrino oscillations? The electron neutrino flavor state is a mixture of at least 2 mass eigenstates:

|νₑ¯¯¯¯¯⟩=cosθ|ν₁⟩+sinθ|ν₂⟩

where, |ν₁⟩ is the first mass eigenstate and |ν₂⟩ is the second mass eigenstate. I assume that the mass of both is significantly different. |νₑ¯¯¯¯¯⟩ is the electron neutrino flavor eigenstate. As far as I understand the mass of the flavor eigenstate is not known and upon measurement it would project on one of the 2 possible mass eigenstates. So what are they measuring actually?

Answer 1

Neutrino oscillations occur when neutrinos change spontaneously from one flavor to another.

The mass of the electron neutrino is extremely small, less than 1eV. Scientists measure the projection of the flavor eigenstate onto one of the two possible mass eigenstates.

Step-by-step explanation:

Neutrino oscillations occur when neutrinos change spontaneously from one flavor to another. However, for neutrino oscillations to happen, neutrinos must have a non-zero mass.

The electron neutrino flavor state is a mixture of at least two mass eigenstates, |νₑ¯¯¯¯¯⟩=cosθ|ν₁⟩+sinθ|ν₂⟩.

While the mass of the flavor eigenstate is not known, experiments have shown that the mass of the electron neutrino is extremely small, less than 1eV.

This means that when measuring the mass of the electron neutrino, scientists are actually measuring the projection of the flavor eigenstate onto one of the two possible mass eigenstates.