Why More W^+/- than Z^0 in Proton-Antiproton Collisions?

[evilcman]

Can someone give me a qualitative/handwaving argument of
why much more W^+/- boson are produced in proton-antiproton
collisions compared to Z^0 bosons?

PDFs are not enough to explain this I believe, since we will have more
u ubar pairs in the collision than u dbar...

Also if I remember correctly the coupling for the Z-2fermion
vertex is higher with a factor of 1/sin(theta_W). Well the vertices
are kinda different so this is not so simple.

Is there an easy way to guess this or one has to do a full LO calculation
or something?

 

[kaksmet]

First thought, don't know if its the dominant effect.

Z can be produced in the first vertex, but all such vertices can also produce a photon. The photon couples to W's but not to Z and therefore the photon can decay into a pair of W's.

This means that W's can be produced both by u ubar and by u dbar, while Z only get produced by u ubar collisions.

cheers!

 

[Vanadium 50]

1) The Z is heavier.

2) The Z's vector coupling to quarks is less than the W's.