Homework Help: Feynman Diagram of Neutron-Antineutron reaction

1. Jan 30, 2013

JamesM86

1. The problem statement, all variables and given/known data

Is the following reaction possible? If so, by what force? Draw (one of, if applicable)the lowest order Feynmann diagrams for the process.

n + n-bar --> ∏+ + ∏- + ∏0

2. Relevant equations

N/A

3. The attempt at a solution

This process, it seems to me, should be possible. It doesn't violate conservation of energy, charge, or baryon number. However, when I draw the feynmann diagram, I notice something odd.

It is apparently possible to simply rearrange the quarks and antiquarks of the neutron and antineutron into the three pi mesons, without actually making any vertices in the diagram. This would suggest that the process isn't actually mediated by any kind of force...

This can't be right, and I'm quite confused. Thank you for any help!

2. Jan 30, 2013

Simon Bridge

It's a nuclear interaction - try comparing with the other diagrams you have for interactions between nucleons.

3. Jan 31, 2013

JamesM86

I don't "have" any other such diagrams. We have discussed this sort of interaction in detail yet.

4. Jan 31, 2013

Simon Bridge

Ah - in which case you'd want to look for some online.
You really need to spend some time on ordinary inter-nucleon interactions before you deal with something like this.

Wikipedia has some examples in it's entry on the strong nuclear interaction.

5. Jan 31, 2013

JamesM86

That wikipedia article does have the feynman diagram for the stron interaction between a proton and a neutron. I have seen it before.

So in this diagram I'm drawing, do I need to just add gluons and interactions? My reservation is that I'm supposed to be drawing the lowest order diagrams that I can draw, and so I don't understand why I need to arbitrarily add gluon vertices, or where exactly it would be legitimate to do so.

6. Jan 31, 2013

Simon Bridge

Take a look at the animation further down - it shows you why you need the extra gluon interactions. You have to work out how the quarks could get resorted into pions - why not just stay in their neutrons? The simplest possible Feynman diagram, after all, is the one where the particles just pass each other without interacting. Something extra has to be happening.