Feynman diagram; ##\pi^0+\pi^0\rightarrow \pi^++\pi^-##

[pondzo]

Homework Statement

For the reaction below draw three Feynman diagrams, one that proceeds through
exchange of a gluon, one through a photon and one exchanging a weak W-Boson.

$\pi^0+\pi^0\rightarrow \pi^++\pi^-$

Which diagram provides the dominant contribution for this reaction?
Explain how the electromagnetic force can work on an electrically neutral particle like the $\pi^0$.

Homework Equations

The Attempt at a Solution

First of all I'm confused by the composition of the $\pi^0$ meson, do I use $d\bar{d}$ or $u\bar{u}$? I would think that for one neutral pion I use $d\bar{d}$ and the other I use $u\bar{u}$ since this gives the constituent quarks for the products. But then I have no idea how to begin drawing the interaction and how the virtual particle changes the diagram. I apologise since I am very new to Feynman diagrams. Here is an attempt for the W boson:

 

[mfb]

First of all I'm confused by the composition of the $\pi^0$ meson, do I use $d\bar{d}$ or $u\bar{u}$?

You can use either.

The W diagram is fine (what is that to the upper right of the "W"?).