How does beta disintegration work?

[adolphysics]

In beta desintegration, a down quark becomes an up quark by the weak force. We have to add one positive charge to make it work, and it comes from a virtual positron/electron pair. The positron changes the down quark to up quark and the electron scapes. But why does it scape because it's near positivly charged quarks? And why does that positron react with the down quark and not with the positron? (I'm not very good at this, i hope you understand, probably almost everything that i think is wrong but i want to know why)

 

[Orodruin]

This is not a correct description of what is going on. Beta decay is mediated by W bosons and also result in a neutrino.