Pion Decay in QED: Can it Occur via a Virtual Photon?

In summary, the decay of the Pi-0 meson in QED to an electron positron pair can occur through two virtual photons but not through a single virtual photon. This is due to the coupling strength between the pi0 and the photon, which is zero for the single virtual photon diagram. Additionally, the spin and parity of the pi0 state also restricts the number of photons that can be produced in the decay.
  • #1
Rudipoo
32
0
Hi,

I was wondering whether the decay of the Pi-0 meson in QED to an electron positron pair can occur as follows:

Pi-0 -> virtual photon -> e+e-

or does it have to go via

Pi-0 -> two virtual photons -> e+e- (the Feynman diagram has a 'square' of virtual electrons/photons)?

I have a feeling it is forbidden via the first route but I'm unsure why, unless angular momentum has to be conserved within the diagram as well as for the beginning and end states?

Many thanks.
 
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  • #2
More fundamental than that. What is the coupling between the pi0 and the photon?
 
  • #3
The coupling strength is the charge of the up quark multiplied by e, the electronic charge, so (2/3)*e?
 
  • #4
No, that's the coupling to an up quark. What is the coupling to the entire pi0?
 
  • #5
For the diagram that just has the up/anti-up annihilating to a photon I don't know what else the coupling could be...

For the two photon diagram you'd get (2/3*e)+(-2/3*e)=0?!
 
  • #6
Rudipoo, as you say, the π0 is composed of a quark and an antiquark. It's like positronium, only with quarks instead of electrons. And we know the answer: that positronium only decays into two photons.

For π0 the quarks in the ground state have their spins anti-aligned. That is, it's a singlet S state. It has space parity P = -1 (a pseudoscalar) and charge parity C = +1. An n-photon state on the other hand has C = (-1)n. Therefore you can only have an even number of photons, and this holds even in the intermediate state.
 

1. What is Pion Decay in QED?

Pion Decay in QED (Quantum Electrodynamics) is the process in which a pion particle, which is composed of a quark and an antiquark, transforms into a photon. This process is governed by the laws of quantum mechanics and is an important phenomenon in particle physics studies.

2. Can Pion Decay occur via a Virtual Photon?

Yes, Pion Decay can occur via a Virtual Photon. Virtual particles, such as photons, are particles that exist for a very short period of time and are not directly detectable. In Pion Decay, a virtual photon can be created and then quickly decay into two real photons, resulting in the transformation of the pion into two photons.

3. What is the role of Quantum Electrodynamics in Pion Decay?

Quantum Electrodynamics is the theoretical framework that describes the behavior of particles and their interactions through the exchange of photons. In Pion Decay, QED plays a crucial role in understanding the dynamics of the process and predicting its outcomes.

4. What is the significance of studying Pion Decay in QED?

Studying Pion Decay in QED allows scientists to gain a deeper understanding of the fundamental laws and principles governing the behavior of particles and their interactions. It also has practical applications, such as in the development of technologies such as particle accelerators.

5. Are there any ongoing research or experiments related to Pion Decay in QED?

Yes, there are ongoing research and experiments related to Pion Decay in QED. For example, scientists are currently conducting experiments at facilities such as the Large Hadron Collider to study the properties of pions and their decays, which can provide valuable insights into the behavior of particles at a fundamental level.

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