Parity of a system composed by 2 particles

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Discussion Overview

The discussion revolves around the concept of parity in a system composed of two particles, specifically addressing the formula for total parity and the implications of relative angular momentum. Participants explore the definitions and relationships between angular momentum, particle interactions, and the implications of different wave states (S-wave, P-wave, etc.).

Discussion Character

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

Main Points Raised

  • One participant states that the total parity for a two-particle system is given by the product of their intrinsic parities multiplied by (-1) raised to the power of the relative angular momentum, L.
  • Another participant clarifies that "relative" angular momentum refers to the momentum of the two particles considered as orbiting around each other.
  • A participant questions the practical implications of this concept, specifically in the context of a pion being captured by deuterium and the associated wave state.
  • Participants discuss the nomenclature of wave states, indicating that S-wave corresponds to L=0, P-wave to L=1, and D-wave to L=2.
  • One participant expresses confusion about the relationship between wave states and relative angular momentum, seeking clarification on how S-wave implies L=0.
  • A later reply confirms that stating a system is in a specific wave state directly indicates the value of relative angular momentum.
  • Another participant notes that while the wave state can indicate L, there are cases where relative angular momentum is constrained by other factors, such as total angular momentum and parity conservation.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of wave states and their relationship to relative angular momentum. However, there remains some uncertainty regarding the practical implications of these concepts in specific scenarios, such as the interaction between a pion and deuterium.

Contextual Notes

Limitations include the potential for different processes to occur with varying values of L, which may not be fully addressed in the discussion. The relationship between total angular momentum and parity conservation is also noted as a factor that could influence the outcomes.

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I have read that for a system of 2 particles, the total parity is given by:

P=P_1 P_2 (-1)^L where

- P_1, P_2= insisec parity of particle 1, 2

- L= relative angular moment

what's the meaning of "relative angular moment"? Do I have to add the l numbers of the two particles? And what if I have 3 particles?

Many thanks
 
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L is the "relative" angular momentum, which means that is the momentum of the system of the two particles "orbiting around each other" if considered as a whole.

If you have three particles you need to first study two of them and obtain the corresponding system and then compose this last system with the third particle.
 
Einj said:
L is the "relative" angular momentum, which means that is the momentum of the system of the two particles "orbiting around each other" if considered as a whole.

If you have three particles you need to first study two of them and obtain the corresponding system and then compose this last system with the third particle.

Thanks for your answer. But I have no ideas about what I have to do in practice... For example, let's consider a pion and a deuterium. I know that the pion is captured in s-wave by the deuterium and it was told me that (-1)^L =1, but I don't understand why. Could you help me?
 
The nomenclature is S-wave (L=0), P-wave (L=1), D-wave (L=2), etc.
 
I imagined it... but I haven't understood what is a "S-wave". The fist - and last - time that I have heard it, the prof said "The deuterium captures the pion in S-wave". Could you explain me briefly in which way "S-wave" and L (relative angular moment) are related? Does "S-wave" imply that the relative angular moment is 0?
 
Yes, it's just a way of saying it. If you say that a system is in S/D/P-wave you are simply saying that the relative angular momentum of this system is L=0/1/2, nothing more. It's a nomenclature borrowed from atomic physics.
 
Oh, so many thanks! :)

And so, if the prof hadn't said that the pion is captured in S-wave, I wouldn't be able to say that L=0, isn't it?
 
Generally speaking yes. In some cases the relative angular momentum is constrained by total angular momentum and parity conservation.

However, most of the times, a certain process can happen with different L. The distinction between the different cases must be made experimentally.
 
Thanks again!
 

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