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Results tagged with helicity
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user 44126
In particle physics, helicity is the projection of the angular momentum onto the direction of momentum. For massless spin-1⁄2 particles, helicity is equivalent to the chirality operator multiplied by $\hbar/2$, so may be used for related chirality questions as well.
8
votes
How can helicity be conserved but chirality not?
However, the evolution of its helicity is governed by conservation of angular momentum. … But to conserve angular momentum you must have (in helicity) to right-handed or two left-handed decay products. …
rob♦
- 94.2k
1
vote
Addition of spin angular momentum for massless particles
Here's the algorithm for finding Clebsch-Gordan coefficients:
Start with a maximally aligned state like
$\big|S,M = 2,2\big> = \big| m_1,m_2 = 1,1\big>$
Operate repeatedly with the lowering operato …
rob♦
- 94.2k
0
votes
Accepted
Accounting for photon spin angular momentum in general relativity for two (anti-)parallel ph...
I think general relativity is a distraction here, because the spin-exchange interaction in electromagnetism is local.
The photon interacts with electric charges and magnetic dipole moments, but the ph …
rob♦
- 94.2k
27
votes
A thought experiment about neutrinos
Since there are now several comments and answers pointing out that chirality, unlike helicity, is invariant under boosts, I should clarify. … You can absolutely change whether (or better, how much) a particle with Dirac mass participates in the weak interaction by flipping its helicity; I spent fifteen years doing this with polarized beams of …
rob♦
- 94.2k
4
votes
If helicity of photons is +1 then the light is right- or left-circularly polarized?
For historical reasons, the optics convention and the helicity convention are opposite. … A "positive helicity" particle is one whose momentum goes in the direction of the thumb. Now point that thumb at your face, and observe that the fingers go to your left. …
rob♦
- 94.2k