# Nutrino Mass and Oscillation problem

1. Oct 22, 2012

### FeynmanIsCool

I have a question:

Excuse me if this has been answered on here. Neutrino's are said to travel at the speed of light. As we know anything with mass cannot travel at c. We have also observed neutrino "influxes" at the same time we observe a super nova, which means that neutrino's and photons are traveling at the same speed.

BUT

What about Neutrino oscillations? Neutrino's are said to change from electron neutrino --> tau neutrino --> muon neutrino, and so on. In order for these oscillations to happen, the neutrino must experience time, because these oscillations are time dependent. But we also know due to Relativity that time stops when you travel at c. If time was "stopped" for a neutrino, how can it oscillate?
Has this dilemma been answered already, and I have not done enough research?

2. Oct 22, 2012

### Staff: Mentor

Where?
"Close to the speed of light" is not "at the speed of light".

Nearly the same, which is a completely different statement. The difference is too small to observe it with current experiments.

3. Oct 22, 2012

### FeynmanIsCool

"In the early 1980s, first measurements of neutrino speed were done using pulsed pion beams (produced by pulsed proton beams hitting a target). The pions decayed producing neutrinos, and the neutrino interactions observed within a time window in a detector at a distance were consistent with the speed of light. This measurement was repeated in 2007 using the MINOS detectors, which found the speed of 3 GeV neutrinos to be 1.000051(29) c at 68% confidence level, and at 99% confidence level a range between 0.999976 c to 1.000126 c. The central value is higher than the speed of light and is consistent with superluminal velocity; however, the uncertainty is great enough that the result also does not rule out speeds less than or equal to light at this high confidence level" -wiki on neutrinos

so what is the speed?? is it close to light or what?

4. Oct 22, 2012

### FeynmanIsCool

"The same observation was made, on a somewhat larger scale, with supernova 1987A (SN 1987A). 10-MeV antineutrinos from the supernova were detected within a time window that was consistent with a speed of light for the neutrinos. So far, the question of neutrino masses cannot be decided based on measurements of the neutrino speed." - wiki on neutrinos

5. Oct 22, 2012

### FeynmanIsCool

Im not paying any attention to claims that neutrinos can travel faster than C, I know all those claims are miss calculations, and have since been proven wrong, so you don't need to bring that up.

6. Oct 22, 2012

### Staff: Mentor

With neutrino masses of the order of some milli-electron volt and neutrino energies of some MeV, the neutrino speed is about c*(1-10-18) or 0.999999999999999999 c.

SN1987 A was about 150,000 light years away, the sub-luminal speed corresponds to a time difference of the order of some microseconds.
No experiment has the sensitivity to see that small deviation from c, even if the deviation is crucial for mixing.

7. Oct 22, 2012

### FeynmanIsCool

ok, thanks! So basically, it comes down to: We know that neutrino's don't travel at c, but our experiments don't have the sensitivity to tell how close to c neutrino's are traveling....slightly un-settling

8. Oct 22, 2012

### bossman27

I believe the general concensus at this point is that neutrinos do have mass. They are almost massless, and travel at a velocity very near C. But as you mentioned, the fact that they oscillate between flavors implies V<C. Although this is the generally accepted stance, there are apparently types of Lorentz-violations in some quantum gravity theories that could allow for neutrino velocity at or above C. My understanding (someone correct me if I'm wrong), is that they aren't very viable at this point (in the sense of being testable/falsifiable), but you might find them interesting nonetheless: http://en.wikipedia.org/wiki/Lorentz-violating_neutrino_oscillations#General_predictions

9. Oct 22, 2012

### Staff: Mentor

Right.
And without a method to produce collimated low-energy neutrinos or without very distant supernovae, I don't expect changes in that respect.

Direct mass measurements (beta decay) could measure the electron neutrino mass, and mixing experiments can give mass differences.

10. Oct 23, 2012

### snorkack

So, do gamma ray flashes emit neutrinos?

11. Oct 23, 2012

### Staff: Mentor

http://arxiv.org/abs/0907.2227
The bad news: If there are neutrinos, they are even more high-energetic, and they can be produced at a different time.