Neutrinos: Mass & Spin Explored

[Reshma]

Do neutrinos have mass and spin?

 

[dextercioby]

Do neutrinos have mass and spin?

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.

 

[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 learned 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 existence 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 theorized to conserve energy in the weak interactions.

 

[mathman]

Neutrinos as noted above have a very small mass. Coming out of a supernova they are traveling 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.

 

[Jake]

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

 

[dextercioby]

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

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.

 

[Andrew Mason]

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

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

 

[Nereid]

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 learned 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 existence 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 theorized to conserve energy in the weak interactions.

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.

 

[dextercioby]

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

Which part was it unclear??This one??

To quote from the booklet from PDG,dating July 2004

Daniel.

 

[Andrew Mason]

Which part was it unclear??This one??

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

AM

 

[Enos]

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

 

[Nereid]

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

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).

 

[Enos]

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

 

[dextercioby]

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

AM

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


Daniel.

 

[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?

 

[taeth]

mνe < 2.5 eV
νμ < 170 keV
ντ < 18 MeV

This is what I always thought it was...

 

[dextercioby]

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

Daniel.

 

[dextercioby]

mνe < 2.5 eV
νμ < 170 keV
ντ < 18 MeV

This is what I always thought it was...

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

Daniel.

 

[taeth]

http://en.wikipedia.org/wiki/Neutrino you really hate me... but with what I've said lately for good reason.

 

[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.

 

[taeth]

That wasn't my original source I remember reading it in a book I have... its too hard to link things from books so I just found a site with comparable numbers.

 

[Haelfix]

I would say the majority of people working in Neutrino physics expect they acquire a Majorana mass via the seesaw mechanism. Various Susy/nonSuSy GUTs can give the correct mechanism up to order of magnitude for the right handed 'sterile' Neutrinos.

 

[Andrew Mason]

mνe < 2.5 eV
νμ < 170 keV
ντ < 18 MeV

These are not figures for rest mass. They represent relativistic mass. The Wikipedia page you referred to: http://en.wikipedia.org/wiki/Neutrino makes this clear:

"If the total mass of all three types of neutrinos exceeded 50 electron volts (per neutrino), there would be so much mass in the universe that it would collapse. This limit can be circumvented by assuming that the neutrino is unstable; however, there are limits within the Standard Model that make this difficult."

Recent experiments put the total rest masses of all three neutrinos at less than 1 eV.

AM

 

[taeth]

I didn't think they had equated the rest mass of neutrinos yet...

 

[Mk]

http://physicsweb.org/articles/world/11/7/3/1
This article may be of interest.

 

[jtbell]

These are not figures for rest mass. They represent relativistic mass.

They can't represent relativistic mass. Relativistic mass depends on energy. A neutrino with an energy of 50 GeV, such as have been produced in accelerator experiments, has a relativistic mass of 50 GeV/c^2.

 

[Andrew Mason]

They can't represent relativistic mass. Relativistic mass depends on energy. A neutrino with an energy of 50 GeV, such as have been produced in accelerator experiments, has a relativistic mass of 50 GeV/c^2.

The figures provided refer to solar neutrinos, I believe. They are expressed in relativistic mass (in units of eV/c^2).

AM