How exactly does the pion decay through the weak force?

In summary, the pion(+)n is made up of an up quark and a down antiquark and can emit a W+ boson, which then turns into a muon and a muon-neutrino. This reaction can go in both directions, with a pion(+) turning into a W+ boson and then back into a pion(+). The up quark and down antiquark interact to produce the W+ boson, according to the assumption in the standard model. This process is very short-lived and occurs at a high concentration of energy.
  • #1
Simfish
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So the pion(+)n is made up of an up quark and a down antiquark. And somehow, it emits a W+ boson, which then turns into a muon and a muon-neutrino.

From the Wiki article, "W bosons can decay to a lepton and neutrino or to an up-type quark and a down-type quark."

Does this mean that the reaction can go in both directions? Meaning that a pion(+) could turn into a W+ boson, which then turns back into a pion(+)?

And how do the up quark and down antiquark interact to produce that W+ boson?
 
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  • #2
Simfish said:
Does this mean that the reaction can go in both directions? Meaning that a pion(+) could turn into a W+ boson, which then turns back into a pion(+)?

How could you tell? The initial state and the final state are the same. How would this be different from the pion just sitting there?

As far as "do the up quark and down antiquark interact to produce that W+ boson", what kind of answer are you looking for?
 
  • #3
How could you tell? The initial state and the final state are the same. How would this be different from the pion just sitting there?

Perhaps there is a phase where you can measure the W+ boson (if that's possible). Alternatively, this could explain why some pions take longer than "usual" to decay. (as opposed to other particles that decay through an irreversible route)

As far as "do the up quark and down antiquark interact to produce that W+ boson", what kind of answer are you looking for?

Basically, I want to know if pion decay is phenomenological. Or in other words, why do up quarks interact with down antiquarks to produce the W+ boson?
 
  • #4
why do up quarks interact with down antiquarks to produce the W+ boson?
This is one of the basic assumptions that go into the standard model, namely that the weak interaction can be described by Wμjμ where jμ is the weak current. The weak current is a sum of terms, each term containing a pair of fermions, either quark plus antiquark or lepton plus neutrino.

I guess the real answer to 'why' is that ultimately no one knows why, but if we make that assumption it agrees with experiment.
 
  • #5
Simfish said:
So the pion(+)n is made up of an up quark and a down antiquark. And somehow, it emits a W+ boson, which then turns into a muon and a muon-neutrino.

From the Wiki article, "W bosons can decay to a lepton and neutrino or to an up-type quark and a down-type quark."

Does this mean that the reaction can go in both directions? Meaning that a pion(+) could turn into a W+ boson, which then turns back into a pion(+)?

And how do the up quark and down antiquark interact to produce that W+ boson?

Informative picture here: http://www.animatedphysics.com/baryon_decay/muon_spin.jpg of the main particles - Pion/Muon/Electron

The boson is around for a much smaller timescale, a high concenetration of energy, around just long enough for the pion to change into a muon.
 

1. What is the weak force?

The weak force is one of the four fundamental forces of nature, along with gravity, electromagnetism, and the strong nuclear force. It is responsible for the radioactive decay of particles and plays a crucial role in the behavior of subatomic particles.

2. How does the weak force differ from other forces?

The weak force is different from other forces in several ways. Firstly, it is the only force that can change the flavor of a particle (e.g. converting a down quark into an up quark). Secondly, it has a very short range, only acting on particles within a distance of about 10^-18 meters. Finally, it is the only force that violates the conservation of parity, meaning it does not behave the same way when particles are mirrored.

3. What is the role of the pion in the weak force?

The pion, or pi-meson, is a subatomic particle that plays a crucial role in the weak force. It is a composite particle made up of a quark and an antiquark, and it is responsible for mediating the weak force between particles. In particular, the pion is involved in the decay of other particles through the weak force.

4. How exactly does the pion decay through the weak force?

The pion decays through the weak force by releasing a W boson, which then decays into either an electron and an electron antineutrino, or a muon and a muon antineutrino. The specific decay mode depends on the type of pion (π- or π+). This process follows the rules of the Standard Model of particle physics, which describes the behavior of particles and their interactions.

5. Why is the study of pion decay important?

The study of pion decay is important for several reasons. Firstly, it provides insights into the weak force and its behavior, which is crucial for understanding the behavior of subatomic particles. Secondly, it helps to validate the Standard Model and its predictions. Additionally, pion decay has practical applications, such as in medical imaging techniques like positron emission tomography (PET).

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