Predicting the charge of a W boson

[tmonk]

For my Physics exam, I need to know 3 Feynman diagrams: beta-plus/minus decay, proton electron capturing, and neutrinos interacting with matter.

I know that theres a W- in \beta- decay, W+ in \beta+ decay, which seems logical.

However, in proton electron capture there is a W+ boson, and in a neutron-neutrino collision there is a W-. There seems to be no rule governing the charge of the boson.

If there is, could someone please let me know!

[ansgar]

p + e -> n + nu

?

then the electron would turn into a W- and a nu where the W- interacts with the quark

[tmonk]

p + e -> n + nu

?

then the electron would turn into a W- and a nu where the W- interacts with the quark

I thought it was a W+ boson in this case, which turns the u into a d?

[ansgar]

u plus w+ gives something with +5/3 charge... right?

[filegraphy]

When a W negative boson is emitted from a neutron it forms an electron and an electron anti neutrino. This causes the down quark from the neutron to turn into a up quark to form a proton. This is the energy released in radioactive decay. That is all I can do. http://en.wikipedia.org/wiki/Weak_interaction