# Mass of neutrinos

1. Jan 16, 2005

### Reshma

Do neutrinos have mass and spin?

2. Jan 16, 2005

### dextercioby

They definitely have spin.As for mass,apparently there are no sources left which indicate zero mass.
To quote from the booklet from PDG,dating July 2004
$$m_{\nu_{e}}<3eV$$

$$m_{\nu_{\mu}}<0.19MeV$$

$$m_{\nu_{\tau}}<18.2MeV$$

Daniel.

3. Jan 16, 2005

### kirovman

I was under the impression that neutrinos from supernova reached the earth before the photons did....because the photons are slowed by the gases and plasmas of space, and neutrinos rarely interact.
Forgive me if I'm wrong, this is something I learnt about 4 or 5 years ago, so it's not fresh.
Some scientists were doing an experiment to measure the weak force or prove the existance of their mediator particle, I believe they used an underground reservoir of Chlorine or a compound of it. Anyway, they detected the influx of neutrinos a few hours before they observed a supernova.

So maybe they have mass, but they still seem to travel pretty fast.

Trouble with neutrinos, it's difficult to observe them. They were originally theorised to conserve energy in the weak interactions.

4. Jan 16, 2005

### mathman

Neutrinos as noted above have a very small mass. Coming out of a supernova they are travelling very close to the speed of light. Because they are difficult to measure, it took a long time before physicist were able to show definitely that they did have a non-zero mass.

5. Jan 16, 2005

### Jake

What would they have been if they had no mass anyway, just another form of electromagnetic wave?

6. Jan 16, 2005

### dextercioby

Not exactly.Technically,they would have been massless quanta of a neutrino field,which is a spin 1/2 field.The trick is that these neutrinos,cf.photons,they don't have 2 helicity states,but only one.

I believe the problem of massive right-handed neutrinos is still open...

Daniel.

7. Jan 16, 2005

### Andrew Mason

This seems like an awfully large upper limit. Do you have a reference?

This source seems to put the sum of all three rest masses at less than .71 eV: http://xxx.lanl.gov/PS_cache/hep-ph/pdf/0302/0302191.pdf

AM

Last edited by a moderator: Apr 21, 2017
8. Jan 16, 2005

### Nereid

Staff Emeritus
I'm not at all sure there was much of a time difference ... the photons 'first' detected were well after the star had gone SN (when someone in NZ or Australia actually noticed there was a star in the LMC that they didn't recognise). In any case, the neutrinos would escape the SN before EM, because the (dying) star becomes transparent to neutrinos as soon as the shock wave gets just above the core ... that wave takes some time to reach the surface of the star, when the EM finally breaks loose.

Google on 'neutrino oscillations'; as usual in HEP, things are a little more complicated than what you read in the popular press.

9. Jan 16, 2005

### dextercioby

Which part was it unclear??This one??
Daniel.

Last edited by a moderator: Apr 21, 2017
10. Jan 17, 2005

### Andrew Mason

When I asked for the reference, I meant: where can I find it?

AM

11. Jan 17, 2005

### Enos

Close to the speed of light requires mass no? At the speed of light is the classification of massless no?

12. Jan 17, 2005

### Nereid

Staff Emeritus
An object with mass cannot travel at c; a massless particle must travel at c. 'Weighing' neutrinos is very difficult to do, esp for the mu and tau kinds. Until neutrino oscillation was confirmed (observations and experiments), we couldn't say whether neutrinos have mass; now we can say that at most only one flavour can be massless. However, like all 'conclusions' in science, this is tentative, and assumes that several theories are good representations of 'reality' (whatever that is).

13. Jan 17, 2005

### Enos

don't pay attention to the "no?" in my statements. Just felt like adding them to bring an extra spark into my words.

14. Jan 17, 2005

### dextercioby

If you don't have the booklet,then their website will do it:
website

Daniel.

15. Jan 17, 2005

### houserichichi

Rather than start a new thread I'll ask it right here...for those who have ordered the booklets from the PDG, how long does it typically take for them to arrive? I ordered mine in late November but they've yet to come in - am I being too impatient?

16. Jan 17, 2005

### taeth

mνe < 2.5 eV
νμ < 170 keV
ντ < 18 MeV

This is what I always thought it was...

17. Jan 17, 2005

### dextercioby

Actually i got it as a gift from the faculty...Supposedly helping me with my thesis... :yuck:
I really don't know when they got it... :tongue2:

Daniel.

18. Jan 17, 2005

### dextercioby

Post the source,please...We really don't care what u think... :tongue2: It's better to present the source,so anyone could check it out,if they want to.

Daniel.

19. Jan 17, 2005

### taeth

20. Jan 17, 2005

### dextercioby

I don't hate anyone...I just found curious the part with "thought"...And the fact that u didn't post your source from the first post...

Daniel.