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Confused over neutrinos

  1. Dec 19, 2005 #1
    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 :wink: , do neutrinos constitute the dark matter in the universe?
  2. jcsd
  3. Dec 19, 2005 #2


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    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.

  4. Dec 19, 2005 #3
    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).
    Photons have spin one ! Neutrinos are fermions.
    They have opposite leptonic number. For instance in beta decay, an anti-neutrino is emited with the electron, so that lepton number is conserved.
    Last edited: Dec 19, 2005
  5. Dec 21, 2005 #4
    Thank you Humanino and dextercioby for replying!
    Really? What does this mean qualitatively? Why do they have zero rest mass?
    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 :cool: .
    This fixed helicity allows the neutrino and anti-neutrino to move with the velocity of light c. What does this mean?
  6. Dec 21, 2005 #5
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