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

In summary: However, because neutrinos do not have a definite parity, the transformation of a neutrino's parity is not always conserved. This is seen with beta decay, in which the parity of the anti-neutrino is not always the same as the neutrino's parity.
  • #1
cairoliu
51
3
Wikipedia only tells neutrino spin 1/2, but no tell parity sign: positive or negative?
 
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  • #3
PeterDonis said:
What do you mean by "parity sign"?
Because I know protons, neutron, electron all 1/2+ spin with positive sign of parity, but only know neutrino 1/2 spin.
 
  • #4
cairoliu said:
Because I know protons, neutron, electron all 1/2+ spin with positive sign of parity

Again, what do you mean by "positive sign of parity"? Please give a reference.
 
  • #5
PeterDonis said:
Again, what do you mean by "positive sign of parity"? Please give a reference.
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
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.
 
  • #8
Also, in addition to what Peter said, what do you imagine that the parity transformation of a left-handed neutrino is?
 
  • #9
Orodruin said:
Also, in addition to what Peter said, what do you imagine that the parity transformation of a left-handed neutrino is?
I imagine it as left hand ruled direction of angular momentum vector. right or wrong?
Anyway momentum conserves.
 
  • #10
No, I asked you what you thought the parity transformation of the left-handed neutrino is. Not what the left-handed neutrino is.
 
  • #11
Orodruin said:
No, I asked you what you thought the parity transformation of the left-handed neutrino is. Not what the left-handed neutrino is.
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.
 
  • #12
PeterDonis said:
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.
Thanks for your answer.
Last little confused:
"do not have a definite parity" means parity of neutrino could be +1 or -1 both possible?
 
  • #13
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.
 
  • #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.
 
  • #15
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.
 
  • #16
cairoliu said:
I like to think symbolically and mathematically, and let equation itself tell whether parity conserve.

The equations governing the weak interactions of neutrinos are easily found in textbooks or online.
 

1. Is there a consensus among scientists on the spin-parity of neutrinos?

As of now, there is no consensus on the spin-parity of neutrinos. Some experiments have suggested a spin-parity of 1/2+, while others have suggested a spin-parity of 1/2-. Further research and experiments are needed to reach a conclusive answer.

2. What is the significance of determining the spin-parity of neutrinos?

Determining the spin-parity of neutrinos is important because it will help us better understand the nature of these elusive particles. It can also provide insights into the Standard Model of particle physics and potentially lead to new discoveries and advancements in the field.

3. How do scientists measure the spin-parity of neutrinos?

Scientists use various experimental techniques, such as particle colliders and detectors, to study the interactions of neutrinos. By analyzing the data from these experiments, scientists can infer the spin-parity of neutrinos.

4. Can the spin-parity of neutrinos change?

According to the current understanding of the Standard Model, the spin-parity of neutrinos is a fundamental property and does not change. However, some theories propose the existence of sterile neutrinos that could have different spin-parity states.

5. What are the possible implications if the spin-parity of neutrinos is 1/2+ or 1/2-?

If the spin-parity of neutrinos is 1/2+, it would support the theory that neutrinos are their own antiparticles. On the other hand, if it is 1/2-, it could challenge this theory and lead to new ideas about the nature of neutrinos. It could also have implications for the search for new physics beyond the Standard Model.

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