Why is the W cross section so much larger than the Z cross section?

[JoePhysicsNut]

I had a look at the production cross sections for W/Z at hadron colliders. These differ as a function of energy with the W x-sec being consistently ~10 times larger than the Z cross sections. Why is the W cross section so much larger? I think the coupling strength is similar and the mass difference is not that large either (~10%).

 

[Bill_K]

I don't fully understand the reasoning, but this paper gives the ratio as σ_W/σ_Z ≈ 3.33, and this book derives (Eq. 85) the ratio as

σ_W/σ_Z ~ |V_qq'|²/(v_q² + a_q²)

where V_qq' ≈ 0.97 is the CKM matrix element and a_q = 1/2 and v_q ≈ -0.3 are the neutral current vector and axial vector couplings.

Which works out about right.

 

[Vanadium 50]

What you are probably looking at are not cross-sections but cross-sections times branching fractions.