# In the rest frame of a solar neutrino would I still measure neutrino oscillations

1. Aug 26, 2011

### Spinnor

If I moved in the rest frame of a solar neutrino would I still measure neutrino oscillations?

Thank you for any help!

2. Aug 27, 2011

### Bill_K

Neutrino oscillations are a quantum effect. You can't observe them happening for a single neutrino any more than you can watch Schrodinger's cat oscillate between live and dead. The neutrino state created by a weak decay in the sun is a well-defined neutrino flavor, but not an energy eigenstate. The oscillation takes place because, as the eigenstates that make up the state evolve, the flavor slowly evolves. The only way to observe the flavor of the neutrino is to absorb it with another weak interaction, and of course you can only do this once. Observing the oscillations requires statistics on many neutrinos.

3. Aug 27, 2011

### Spinnor

Thank you! Here was my thinking going to bed. We have a source and a detector a large distance away. I want to know the wave function in a frame of reference that moves from source towards the detector with the average velocity of the neutrinos. In such a reference frame the momentum is minimized (at certain locations) but we are still left with a function that changes in time because of the rest masses? So in such a frame the mass states still interfere in time, flavor changes, we get the same outcomes in different frames? At some distance from the source interference stops because coherence stops? Are we then to think of these mass states being combinations of the flavor states?

Thanks for any help!

Last edited: Aug 27, 2011
4. Aug 27, 2011

Staff Emeritus
Stop...stop...stop...we're all getting off the track here. Go back to elementary QM.

For a neutrino to even have a rest frame, it must be in a mass eigenstate. If it's in a mass eigenstate, the overlap with the flavor eigenstates is a fixed number - it doesn't oscillate.

5. Aug 27, 2011

### Spinnor

I'm trying to think in terms of wave functions. They can be evaluated in different frames. The wave function has information about momentum? Go to a point in such a frame where momentum is minimized. Can we do this?

6. Dec 26, 2011

### cmx

Can a particle be a particle if it does not have a rest frame and invariant rest mass?

Neutrino mass eigenstates can properly be called particles with a rest frame and invariant rest mass, and flavor eigenstates are not particles in this sense. Yet neutrino flavor eigenstates are what we can experimentally observe through space-time events and so we commonly think of them as particles.

Consider beta decay. Neutrino mass eigenstates will have slightly different group velocities, and eventually the wave packets will be spatially separate. Quantum entanglement between the three mass eigenstate wave packets would seem to apply.