What will knowing the mass of neutrinos do for physicists?

[repoman]

I was watching various lectures today about neutrinos and I couldn't exactly figure out how this info will be used.

It seems like that the differences in masses between each type is known (from flavor oscillation) as well as a maximum mass for each from various other observations.

The experiment to detect and measure energies of neutrinoless double-beta decay of xenon is really cool. Hope it works.

https://en.wikipedia.org/wiki/Enriched_Xenon_Observatory

ETA: is neutrinoless double beta eecay the inly way to determine neutrino mass?

Is it possible that that this decay mode does not happen?

 

[Bomb#20]

I was watching various lectures today about neutrinos and I couldn't exactly figure out how this info will be used. ... The experiment to detect and measure energies of neutrinoless double-beta decay of xenon is really cool. Hope it works. ... ETA: is neutrinoless double beta eecay the inly way to determine neutrino mass?

Is it possible that that this decay mode does not happen?

As far as I'm aware, it's never been observed and according to the Standard Model it's impossible. (Double beta decay is well-documented but it normally emits neutrinos.) It would imply lepton number isn't conserved, which would probably imply baryon number isn't conserved and provide a mechanism for proton decay, leading to the end of the universe as we know it.

So the point of the exercise is hopefully to detect new physics that will tell us how to advance beyond the Standard Model. Getting tighter bounds on neutrino masses should help to calculate the probability of neutrinoless double beta decay given various hypothetical proposals for going beyond the Standard Model, so that experiments can support or refute them.

 

[repoman]

So I went to the EXO 200 website and the description for laymen said this:

We want to see neutrinoless double beta decay for two reasons. First, we don't know if the neutrino is its own antiparticle or not, and seeing it would answer this question for sure. Second, we don't know the exact mass of the neutrino and a measurement of the neutrinoless double beta decay half life would allow us to measure the neutrino mass. Even if we don't see neutrinoless double beta decay, a limit on the half life places a limit on the neutrino mass.

So, if neutrinoless double beta (0vBB) does happen not finding it occurs even at very slow rate limits the mass of the neutrino puts an upper bound on its mass through the model they use. The longer the ruled out half-life the smaller the mass, right?

But if (0vBB) doesn't happen it would mean nothing as far as the neutrino mass?

Basically, I don't understand the last sentence of the quote if 0vBB doesn't occur.

 

[Bomb#20]

So I went to the EXO 200 website and the description for laymen said this:

We want to see neutrinoless double beta decay for two reasons. First, we don't know if the neutrino is its own antiparticle or not, and seeing it would answer this question for sure. Second, we don't know the exact mass of the neutrino and a measurement of the neutrinoless double beta decay half life would allow us to measure the neutrino mass. Even if we don't see neutrinoless double beta decay, a limit on the half life places a limit on the neutrino mass.

So, if neutrinoless double beta (0vBB) does happen not finding it occurs even at very slow rate limits the mass of the neutrino puts an upper bound on its mass through the model they use. The longer the ruled out half-life the smaller the mass, right?

That's my understanding, yes. According to Wikipedia the decay rate is proportional to the square of the neutrino mass, and decay rate is inversely proportional to half-life.

But if (0vBB) doesn't happen it would mean nothing as far as the neutrino mass?

Basically, I don't understand the last sentence of the quote if 0vBB doesn't occur.

I think that sentence was only intended to apply to the "0vBB occurs" scenario. If 0vBB doesn't occur there are other ways to constrain neutrino mass. arxiv has a detailed survey of neutrino mass experiments. The bottom line is that lots of experiments have implied upper or lower bounds, and they're all in conflict with one another. It looks like the right values are probably somewhere in the 0.01 eV < neutrino masses < 10 eV range. Some experiments measure the difference between the square of the masses of different types of neutrinos, which means if the masses are at the high end of the range they're nearly identical but if they're at the low end then some are a lot lighter than others. (For comparison, the mass of an electron is about 511,000 eV.)