Neutrino Scattering: F. Diagrams at 1st Order

[Leptone]

Hey...i'm studying the reaction neutrino+antineutrino -> W(+) + W(-)
but i don't understand which are the relevant f. diagrams at first order (semiclassic approximation). Does anyone know which are?

thank you

 

[Bill_K]

At tree level I'd say there's just one. In the crossed channel: ν_e + W^- → e^- → ν_e + W^-

 

[Parlyne]

At tree level I'd say there's just one. In the crossed channel: ν_e + W^- → e^- → ν_e + W^-

Shouldn't there also be a contribution from an s-channel Z?