Feynman Diagrams, exchange particle?

In summary, the Feynman diagram for beta plus decay shows a W+ boson transferring positive charge to the right hand side to balance charges. This is necessary because the positron and neutrino do not directly couple to quarks. The overall reaction is always balanced and the W does not contribute to it as it is an internal (virtual) particle. The direction of the boson is not significant in this process and asking for it in an exam may not be accurate. Charge is conserved at every vertex and particles are not produced to balance charges.
  • #1
CAH
48
0
Exchange Particles are to show the transfer of (for example) +/- charge to the other side so the charges balance. But I don't understand...

Beta plus decay:
p → n + e+ + νe.

This is just an example, the Feynman diagram shows a W+ boson transferring the positive charge to the right hand side, but in the equation: +1 →0 + (+1) + 0
It's all balanced.

So where does the boson come in? Is it to just reinforce the fact that a positron is produced?
 

Attachments

  • image.jpg
    image.jpg
    5.5 KB · Views: 1,656
Physics news on Phys.org
  • #2
The overall reaction is always balanced, and the W does not contribute to it because it is an "internal" (virtual) particle here. There is just no way to write this decay process down without W as the positron and neutrino do not couple to quarks directly. And charge (and also various other numbers) has to be balanced at every vertex.

It is possible to make an effective theory where this "direct" interaction is possible, and it does reasonably well for beta decays, but that does not match our observations in particle accelerators.
 
  • #3
mfb said:
The overall reaction is always balanced, and the W does not contribute to it because it is an "internal" (virtual) particle here. There is just no way to write this decay process down without W as the positron and neutrino do not couple to quarks directly. And charge (and also various other numbers) has to be balanced at every vertex.

It is possible to make an effective theory where this "direct" interaction is possible, and it does reasonably well for beta decays, but that does not match our observations in particle accelerators.
So which direction does the boson go to?
 
  • #4
It is meaningless to talk about directions for virtual particles.
You can say "a W+ goes from the quark vertex to the positron/neutrino vertex", but in the same way you can say "a W- goes from the positron/neutrino vertex to the quark vertex".
 
  • #5
mfb said:
It is meaningless to talk about directions for virtual particles.
You can say "a W+ goes from the quark vertex to the positron/neutrino vertex", but in the same way you can say "a W- goes from the positron/neutrino vertex to the quark vertex".
Where does the negative/positive charge come from/go to, is it basically showing the electron/positron which is produced to balance charges?
 
  • #6
CAH said:
Where does the negative/positive charge come from/go to
I don't think that is a useful question.
Charge is conserved at every vertex. It does not need "directions".
Also, no particles are produced "to balance charges". Unbalanced reactions simply cannot happen.
 
  • #7
I don't think you understand my question.
Also you misunderstood my previous reply i was referring to on the diagram. (Where you draw it from, not in real life)
I know that having a W- boson going to the left has the same effect as a W+ boson going to the right, however marks may be docked in the exam anyway and i still need to know which direction it goes in anyway.
Im sure the W boson comes from the particle that's acting as i have looked into it further.
 
  • #8
CAH said:
however marks may be docked in the exam anyway and i still need to know which direction it goes in anyway.
If the exam is asking for the direction of virtual particles, it is a bad exam.
 
  • #9
mfb said:
If the exam is asking for the direction of virtual particles, it is a bad exam.
'If no arrow on W boson then must be clearly slanting in correct direction. E must have - subscript for second mark. If no clear junctions lose second mark. If no arrows on sides -1.'
 

Attachments

  • image.jpg
    image.jpg
    37.7 KB · Views: 572
  • #10
If they are insisting on arrows on the W, they are wrong. Fermions get arrows. The W is not a fermion.
 

FAQ: Feynman Diagrams, exchange particle?

What are Feynman Diagrams?

Feynman Diagrams are visual representations of particle interactions in quantum field theory. They were developed by physicist Richard Feynman in order to simplify complex calculations and visualize the processes involved in particle interactions.

What is an exchange particle in Feynman Diagrams?

An exchange particle, also known as a virtual particle, is a particle that is not directly observable but is instead used to represent the transfer of energy and momentum between particles in a Feynman Diagram. These particles are responsible for mediating the fundamental forces between particles, such as the strong and weak nuclear forces.

Why are Feynman Diagrams important in particle physics?

Feynman Diagrams are important because they provide a way to calculate and predict the probabilities of particle interactions. They allow physicists to understand and analyze the behavior of subatomic particles, and have been instrumental in the development of the Standard Model of particle physics.

How are Feynman Diagrams drawn?

Feynman Diagrams are drawn using a set of rules and conventions. Each particle is represented by a straight line, with arrows indicating the direction of movement. Interactions between particles are shown as points where the lines meet, and exchange particles are represented by wavy lines. The direction of the arrows and the placement of the points and lines follow specific rules to accurately represent the processes involved.

What is the significance of the direction of time in Feynman Diagrams?

The direction of time in Feynman Diagrams is represented by the direction of the arrows on the lines. Time flows from left to right in the diagrams, with the initial particles on the left and the final particles on the right. This directionality is important in calculating the probabilities of particle interactions and is a fundamental aspect of quantum field theory.

Similar threads

I Confused about particle interactions
Replies
2
Views
1K
A What are some example Feynman diagrams in Yang-Mills theory?
Replies
1
Views
2K
I Feynman Diagrams: ψφ → ψφ | Tips & Advice
Replies
2
Views
2K
I I don't understand this Feynman Diagram
Replies
3
Views
2K
I Confused about Feynman diagrams
Replies
10
Views
3K
A What Are the Possible Decay Processes of the W⁻ Boson?
Replies
1
Views
2K
Attractive Forces from Particle Exchange
Replies
2
Views
3K
A Are unstable particles ever really external lines in QFT?
Replies
3
Views
1K
What is an Exchange Particle? A-Level Physics Explained
Replies
2
Views
3K
I Confused about virtual particles
Replies
4
Views
1K

Hot Threads

Recent Insights

Back
Top