# Cross-section in unitary gauge $e^-e^+\rightarrow ZZ$ process

I've been trying to calculate the cross-section for the process $$e^-e^+\rightarrow ZZ$$ in unitary gauge with vanishing electron mass $$m_e=0$$. I've obtained the following:

I've only determined the cross-section starting from the value $$\sqrt(s)=183 GeV$$ since, in order for the process to occur, I need $$s>4M^2_Z$$, with $$M_Z\approx 90 GeV$$. Anyway, in unitary gauge I would expect that the total cross-section decreases with the energy, which occurs after the peak, but what does that peak correspond to?

• Where is the peak? are you sure you are not seeing your threshold? can you label your plot in better detail there? what width of the Zs have you put in? May 20 '20 at 13:22