# Higgs boson and neutrino mass

1. Jul 5, 2012

### doriannny

In reading through all the info that is coming out from today's big announcement, it seems as they still can't peg the mass of the higgs boson as much of their data comes in the form of decay paths that include neutrinos of unknown mass. My question is whether when they peg the exact mass of the higgs, will they also be able to confer the elusive mass of the neutrino?

2. Jul 5, 2012

### Vorde

Well both experiments pegged a probably mass of the new particle (remember we don't know it's a higgs yet) at about 125 GeV (I think ATLAS' best guess was a little bit higher at about 126 GeV. This is because the decay modes they were looking at did not involve neutrinos.

Even if they did (which some modes might- I don't know), if neutrinos have mass, it is a tiny, tiny amount of mass, enough that even with energy added for velocity I wouldn't expect them to affect the total estimate by much.

3. Jul 5, 2012

### Nabeshin

They surely do have mass, at least two of them. We actually can't say for sure if all three are massive or one is massless and the other two are massive, but that would be an odd state of affairs.

4. Jul 5, 2012

### Vorde

Fair, but my point it still valid. Assuming the tau is the other you mention might not have mass. Is it simply the lack of experimental evidence that illuminates this possibility? Or something else?

5. Jul 5, 2012

### Nabeshin

It's actually not known which of the three is doing what, there's no way to separate them in the measurements. What we measure is the mass difference between two adjacent states, $\Delta m_{12}^2$ and $\Delta m_{23}^2$, the mass difference squared between 1 and 2 and between 2 and 3. Both these quantities are nonzero, which means at least two of them must be massive. If you think about it a bit more, you realize that we actually don't know the ordering of the masses either, simply because this is the only measurement we have. Quite amazing really how little we know about these guys...

6. Jul 5, 2012

### Vorde

How do you measure the mass difference without knowing which is more massive?

7. Jul 5, 2012

8. Jul 5, 2012

### Staff: Mentor

The observation of the Higgs is mainly driven by the decay channels $H \to \gamma \gamma$ and $H \to ZZ* \to 4 l$ (4 leptons), both channels do not include neutrinos.

Neutrinos in decays are very important, and they usually carry a significant fraction of the decay energy. In the decay of a W boson, this is several ten GeV.

In decay channels with neutrinos, it is harder to estimate the mass, but it is not impossible: The energy spectrum of the observable decay products depends on the Higgs mass. Using simulations with different Higgs masses, it is possible to get an estimate for the mass.

9. Jul 5, 2012

### lpetrich

From the neutrinos' mass differences, the maximum neutrino mass is about 0.05 eV, unless the neutrinos' masses are very close to each other. That's far below the mass of the Higgs particle, so neutrino-mass effects will be insignificant.