Right handed or left handed,intrinsic?

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Discussion Overview

The discussion revolves around the concepts of helicity and chirality in particle physics, particularly whether helicity can be considered an intrinsic property of particles. Participants explore the definitions and implications of these terms, examining their dependence on reference frames and motion.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants argue that helicity is not intrinsic because it depends on the direction of motion, which can vary based on the observer's reference frame.
  • Others note that helicity is invariant for massless particles, suggesting a distinction in how helicity is treated for different types of particles.
  • One participant points out that while helicity can change with reference frames for massive particles, it remains constant for massless particles like photons.
  • There is a suggestion that chirality is considered intrinsic in some contexts, but participants question the consistency of this definition, especially in light of reactions that can alter chirality.
  • Another participant raises a question about how to measure chirality if the reference frame changes, indicating uncertainty about the practical implications of these definitions.

Areas of Agreement / Disagreement

Participants express differing views on whether helicity can be considered intrinsic, with some asserting it is not due to its dependence on motion, while others suggest that chirality is intrinsic but not helicity. The discussion remains unresolved with multiple competing views presented.

Contextual Notes

Participants highlight limitations in the definitions of helicity and chirality, particularly regarding their dependence on reference frames and the potential for changes in these properties under different conditions.

ShayanJ
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The helicity of a particle is right-handed if the direction of its spin is the same as the direction of its motion. It is left-handed if the directions of spin and motion are opposite.
from http://en.wikipedia.org/wiki/Chirality_(physics)"

As you can see this definition is depended on the motion of a particle which,of course,is not intrinsic so how can we call helicity,intrinsic?In fact what is the benefit of defining such a thing at all because every particle can move in any direction.
thanks
 
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Although helicity can be defined for any particle it is invariant only for particles with mass zero whose speed is always c in any reference frame.
 
But helicity depends only on the direction of motion,not speed.
 
Yes, I mean the following: In case of a massive particle you can change helicity by changing to a reference system which moves with a higher speed V than the particle in the original system v_0. In the Galilean case this would mean that v in the new system is v_0 -V. If V is greater than v_0, this means that you have changed direction.
In Einsteinian relativity this becomes impossible for massless particles as velocity is no longer additive and especially because c is always c independent of the system of reference.
 
So you can change the helicity of a particle. So what? You can also change the velocity. the energy, the momentum, and many other properties. Why does this one bother you?
 
Shyan said:
from http://en.wikipedia.org/wiki/Chirality_(physics)"
so how can we call helicity,intrinsic?
I can't. Who is 'we'?
 
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If I am reading that correctly: Chirality is intrinsic but helicity is not. Chirality is "handedness" but helicity is not...
 
Handedness,by the definition I found in wikipedia,can't be intrinsic.Also particles can be found to be right handed or left handed.
If above lines are correct,its not reasonable to define handedness.But it is defined.
So I think there should be a problem with the first two lines.
 
In chemistry, we treat chirality of molecules as intrinsic, but that is not strictly true since there are reactions that can change chirality. So for most things, you are correct that chirality and helicity are not invariant. DrDu has explained to you one example where helicity *is* intrinsic, namely photons:

DrDu said:
Yes, I mean the following: In case of a massive particle you can change helicity by changing to a reference system which moves with a higher speed V than the particle in the original system v_0. In the Galilean case this would mean that v in the new system is v_0 -V. If V is greater than v_0, this means that you have changed direction.
In Einsteinian relativity this becomes impossible for massless particles as velocity is no longer additive and especially because c is always c independent of the system of reference.

Doesn't that answer your question?
 
  • #10
Why didn't post #7 end this thread?
 
  • #11
So OK, if chirality is not helicity, then how do we measure it?

Suppose I have a left-handed electron, then I change the reference frame so it moves backwards. How can I determine if it is still left-handed?
 

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