Particle Spin: Definition & Meaning

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    Particle Spin
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Discussion Overview

The discussion centers around the concept of particle spin in physics, particularly the implications of different spin values (s=1, 1/2, etc.) on particle interactions and reactions. Participants explore theoretical aspects, practical implications, and specific scenarios involving particle decay and angular momentum.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants seek clarification on the meaning of particle spin and its notation, specifically regarding how different spin values affect particle behavior.
  • One participant suggests that the conservation of total angular momentum is a critical factor in understanding how spin influences particle decay, noting that a spin-1/2 particle cannot decay into two spin-1/2 particles due to angular momentum constraints.
  • Another participant elaborates on the conditions of a decaying particle at rest, emphasizing that while the total angular momentum is conserved, individual components (spin and orbital) are not necessarily conserved.
  • A participant poses a question about the interaction between two spin-1/2 particles and whether one would acquire orbital momentum, suggesting a scenario involving visualizing their spins in 2D and questioning the implications for their angular momentum.
  • Advanced material on spinors is referenced for those interested in deeper theoretical aspects of the topic.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and curiosity about the implications of spin on particle interactions, with some points of contention regarding the specifics of angular momentum conservation and the behavior of particles with different spins. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Participants express uncertainty regarding the effects of spin on reactions and the conservation of angular momentum, indicating that assumptions about the system's state (e.g., rest frame, orbital momentum) may influence interpretations.

Em!ly
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What is it? And What does it mean when we say s=1, 1/2,...?



Thanx in advance:smile:
 
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jtbell said:
Try this for a start:

http://en.wikipedia.org/wiki/Spin_(physics)

If you still have questions after reading this, feel free to come back and ask! :smile:

Thanx, but I read it before.:confused: I just can't get it how it effects on reactions. I mean what's the difference btw a particle with s= 1/2 and a particle with s=1?
 
Em!ly said:
What is it? And What does it mean when we say s=1, 1/2,...?
Thanx in advance:smile:

Check out this thread

marlon
 
Em!ly said:
I just can't get it how it effects on reactions.

Probably the most important way that particle spin affects reactions like decays is that the total angular momentum of a system is conserved in any reaction. This means, for example, that a spin-1/2 particle (with angular momentum [itex]\frac{\sqrt{3}}{2}\hbar[/itex]) can't decay into two spin-1/2 particles, because there's no way for the total angular momentum of the particles after the decay to have magnitude [itex]\frac{\sqrt{3}}{2}\hbar[/itex].
 
Let's assume the decaying particle is at rest in the lab frame. This means it has orbital angular momentum 0 and all its angular momentum is due to spin. But the decaying particles, since they're moving, can have both spin (they have to have) and orbital angular momentum. The trick is that neither of the 2 is conserved, but only the total angular momentum.

I hope you see why JT's assertion is correct.

Daniel.
 
If a spin -1/2 particle and a spin +1/2 particle (both with 0 orbital momentum)come together, will one of them always obtain orbital momentum? The way i imagine this in 2D is by having two circles in front of me spining with an angular momentum of the same magnitude (1/2) but different directions (one + and one -). In this scenario i would expect one of the particles to start orbiting the other, though i think depending on reference point we can always choose to see either one as orbiting the other. In any case it seems one of these objects would acquire orbital momentum, what happens to their angular momentum? Does the angular momentum of both particles change or does it stay the same?
 
Thank you so much!:smile:
 

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