Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Is neutrino spin-parity 1/2+ or 1/2-?

  1. Dec 18, 2017 #1
    Wikipedia only tells neutrino spin 1/2, but no tell parity sign: positive or negative?
     
    Last edited: Dec 18, 2017
  2. jcsd
  3. Dec 18, 2017 #2

    PeterDonis

    Staff: Mentor

    What do you mean by "parity sign"?
     
  4. Dec 18, 2017 #3
    Because I know protons, neutron, electron all 1/2+ spin with positive sign of parity, but only know neutrino 1/2 spin.
     
  5. Dec 18, 2017 #4

    PeterDonis

    Staff: Mentor

    Again, what do you mean by "positive sign of parity"? Please give a reference.
     
  6. Dec 18, 2017 #5
    Jπ always comes together, if Jπ = 1/2+, it means spin = 1/2, parity = +1.
    I need know neutrino's Jπ, 1/2+ or 1/2- ? At least J = 1/2 is sure, but π = +1 or -1?
     
  7. Dec 18, 2017 #6
  8. Dec 18, 2017 #7

    PeterDonis

    Staff: Mentor

    Ok, then the answer is that neutrinos do not have a definite parity, since neutrinos only interact via weak interactions and weak interactions do not conserve parity.
     
  9. Dec 18, 2017 #8

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    Also, in addition to what Peter said, what do you imagine that the parity transformation of a left-handed neutrino is?
     
  10. Dec 18, 2017 #9
    I imagine it as left hand ruled direction of angular momentum vector. right or wrong?
    Anyway momentum conserves.
     
  11. Dec 18, 2017 #10

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    No, I asked you what you thought the parity transformation of the left-handed neutrino is. Not what the left-handed neutrino is.
     
  12. Dec 18, 2017 #11
    Sorry, no idea, please teach me.
    For the neutron decay: n -> p + e + anti-neutrino
    If parity of anti-neutrino = +1, then left = +1 = right = (+1)*(+1)*(+1) = +1.
    But parity not conserved in beta decay weak interaction, then it seems the parity of anti-neutrino = -1, then left not equal right. Just confused.
     
  13. Dec 18, 2017 #12
    Thanks for your answer.
    Last little confused:
    "do not have a definite parity" means parity of neutrino could be +1 or -1 both possible?
     
  14. Dec 18, 2017 #13

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    It means that it does not make sense to talk about the parity of a neutrino in the way you are imagining. Weak charged current interactions only couple to left-handed particles, which break parity maximally. There are no right-handed neutrinos in the standard model.
     
  15. Dec 18, 2017 #14
    I like to think symbolically and mathematically, and let equation itself tell whether parity conserve. Therefore if there is a value for neutrino parity, then beta decay equation can mathematically show non-conservation of parity, not by fuzzy words.
     
  16. Dec 18, 2017 #15

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    There is nothing about fuzzy words in the standard model. It is a well defined theory. That you do not understand that some concepts that you have learned previously are not applicable to weak decays does not mean that weak decays are non-mathematical.
     
  17. Dec 18, 2017 #16

    PeterDonis

    Staff: Mentor

    The equations governing the weak interactions of neutrinos are easily found in textbooks or online.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Is neutrino spin-parity 1/2+ or 1/2-?
  1. Uuu in spin 1/2 config (Replies: 11)

Loading...