Feynmann diagram for beta decay, direction of arrows confusion

In summary, beta minus decay is a reaction where a neutron changes into a proton, releasing a W- boson which then decays into an electron and an antineutrino. The Feynman diagram for this reaction shows the antineutrino with a backward arrow, which is just a convention due to Feynman. This is because antiparticles can be obtained by acting on particles with the CPT operator, making them "travel backwards in time".
  • #1
UniPhysics90
16
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For beta minus decay, I know the reaction is given by neutron -> proton+electron+anti(electron)neutrino.

This is an image of the Feynman diagram for the reaction:

[URL]http://tmp.kiwix.org:4201/I/280px_Beta_Negative_Decay_svg.png[/URL]

I get that the neutron changes to a proton releasing a w- boson. I think this decays into the electron and anti neutrino. Why then in this diagram is the direction of the arrow of the antineutrino 'backwards' so going back in time?

Thanks
 
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  • #2
UniPhysics90 said:
I get that the neutron changes to a proton releasing a w- boson. I think this decays into the electron and anti neutrino. Why then in this diagram is the direction of the arrow of the antineutrino 'backwards' so going back in time?

Thanks

It's just a convention due to Feynman. Particles are drawn with forward arrows, while antiparticles are drawn with backward arrows. The physical motivation for this is that the antiparticle can be obtain by acting on the particle with the CPT operator. So in a sense, the antiparticle is a particle "traveling backwards in time".
 
  • #3
fzero said:
It's just a convention due to Feynman. Particles are drawn with forward arrows, while antiparticles are drawn with backward arrows. The physical motivation for this is that the antiparticle can be obtain by acting on the particle with the CPT operator. So in a sense, the antiparticle is a particle "traveling backwards in time".

Thanks, if it's just a convention, I'm happy enough with what it shows :)
 

What is a Feynmann diagram for beta decay?

A Feynmann diagram for beta decay is a visual representation of the interactions between particles during the process of beta decay. It shows the initial and final states of the particles involved, as well as the exchange of a virtual particle responsible for the decay.

How do I interpret the direction of arrows in a Feynmann diagram for beta decay?

The direction of arrows in a Feynmann diagram for beta decay represents the flow of particles in time, with the arrows pointing from the initial state to the final state. This means that particles with an arrow pointing towards them are incoming, while particles with an arrow pointing away from them are outgoing.

Why is there confusion about the direction of arrows in a Feynmann diagram for beta decay?

There is often confusion about the direction of arrows in a Feynmann diagram for beta decay because the arrows can be interpreted in two different ways. One interpretation is based on the flow of particles in time, while the other is based on the charge of the particles involved. This can lead to confusion, especially when dealing with neutral particles.

How can I determine the correct direction of arrows in a Feynmann diagram for beta decay?

To determine the correct direction of arrows in a Feynmann diagram for beta decay, you can use the conservation laws of energy, momentum, and charge. These laws dictate that the initial and final states of the particles must have the same total energy, momentum, and charge. By using these laws, you can determine the correct direction of arrows and ensure that your diagram is accurate.

Are there any exceptions to the direction of arrows in a Feynmann diagram for beta decay?

Yes, there are a few exceptions to the direction of arrows in a Feynmann diagram for beta decay. One exception is the case of annihilation, where an electron and a positron collide and produce two photons. In this case, the arrows of the incoming particles are reversed, as the initial state is actually the final state in terms of time. Another exception is when a neutral particle is involved in the decay, in which case its arrow can be interpreted in either direction.

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