How Do I Draw a Feynman Diagram for e+e- → VeVe?

[Bowenwww]

Feynman Diagrams! Please Help!

Hi guys!

I've been asked to draw a scattering and annihilation Feynman diagram for the following scenario:

e⁺e^- → V_eV_e (The second Ve is an anti-neutrino just couldn't figure how to put the bar on! :P

I've tried it and I'm convinced the mediating operator is a photon via the electromagnetic force but I don't see where it can produce two neutrinos :S Unless it's a different mediator?

Anyways any help would be appreciated!

thanks guys!

Karly xoxo

 

[tiny-tim]

Hi Karly!

… I'm convinced the mediating operator is a photon via the electromagnetic force …

But can neutrinos feel the electromagnetic force?

 

[Bowenwww]

No because they have no charge :) do both sides have to be affected by the mediator? That might be a stupid question I'm sorry but I don't know

If they do then this must be via a W boson?

Am I right?

K xoxo

 

[tiny-tim]

No because they have no charge :) do both sides have to be affected by the mediator?

any vertex a fermion (in this case, a neutrino) is joined to must have a boson that "mediates" a force that the fermion feels

If they do then this must be via a W boson?

W or Z (or both) … you decide!

 

[Bowenwww]

But the total charge on the LHS is zero, as is the charge on the RHS so surely it's a Z boson?

Or am I being silly?

Karly xoxox

 

[tiny-tim]

i don't like this LHS RHS way of looking at it

this is an exercise on Feynman diagrams, so look at the vertices …

what happens if the two electrons are joined to the same vertex?

what happens if the two electrons aren't joined to the same vertex? ​

 

[Bowenwww]

Well surely if both the electron and the positron are joined to the same vertex then they have annihilated into a mediator, no? And if they are not then they have simply scattered off each other via the exchange of a mediator?

God I hate this, I know I'm being really stupid but thank-you for your help <3

K xoxo

 

[tiny-tim]

Well surely if both the electron and the positron are joined to the same vertex then they have annihilated into a mediator, no? And if they are not then they have simply scattered off each other via the exchange of a mediator?

yes and yes

but i still think it would be easier if you stuck to considering each individual vertex …

in the first case (the stick-man diagram), there are two ingoing fermions at one vertex, and two outgoing fermions at the other vertex, and in each their charge adds to 0

in the second case (the H-diagram), there is one ingoing fermion and one outgoing fermion at each vertex, and in each case their charge difference is not 0

sooo … ? ​