Unraveling the Mysteries of Neutrinos: Spin, Mass, and Their Role in Dark Matter

[Reshma]

Neutrinos are emitted during the beta-decay process.
Neutrinos definitely have spin. Do neutrinos have mass? Most texts say neutrinos have zero or negligible rest mass. But Neutrinos travel with the speed of light. So how can any particle with finite mass travel with the speed of light? If so how would it make neutrinos different from an electromagnetic wave?

A neutrino has spin 1/2. An anti-neutrino also has spin 1/2. How is it possible to distinguish a neutrino from an anti-neutrino?

Lastly, just out of curiosity , do neutrinos constitute the dark matter in the universe?

 

[dextercioby]

For the last question: maybe.

Chirality is the answer to the penultimate.

If they have mass, then their speed should be less than c, obviously.

Daniel.

 

[humanino]

Do neutrinos have mass?

It seems they do ! The number of neutrinos we receive from the sun indicates neutrinos oscillate between different flavors. This indicates they cannot all have the same mass (so they cannot all be massless).

If so how would it make neutrinos different from an electromagnetic wave?

Photons have spin one ! Neutrinos are fermions.

How is it possible to distinguish a neutrino from an anti-neutrino?

They have opposite leptonic number. For instance in beta decay, an anti-neutrino is emited with the electron, so that lepton number is conserved.

 

[Reshma]

Thank you Humanino and dextercioby for replying!

It seems they do ! The number of neutrinos we receive from the sun indicates neutrinos oscillate between different flavors. This indicates they cannot all have the same mass (so they cannot all be massless).

Really? What does this mean qualitatively? Why do they have zero rest mass?

If they have mass, then their speed should be less than c, obviously.

My book says neutrinos exhibit handedness similar to a screw. A neutrino has spin always anti-parallel to its momentum while an anti-neutrino has spin parallel to its momentum. So, neutrino is a left handed particle and an anti-neutrino is right-handed particle .
This fixed helicity allows the neutrino and anti-neutrino to move with the velocity of light c. What does this mean?

 

[Norman]

I found a great lecture online from Michael Shaevitz from Columbia University on Neutrino Physics:

http://www.nevis.columbia.edu/~shaevitz/talks/NeutrinoLectureWriteup.pdf

I thought it was well written.
Cheers,
Ryan