Then if the collision happens at energy of about Z boson mass, i.e. sqrt(s) ~= m(Z), the s-channel dominates. But depending on the kinematic phase space of the interaction, you might have a situation where the t-channel is dominant. These two cases correspond to the answer by @JamalS: M ~= 1/(s-m^2) @ s~=m^2 VS M ~= 1/(t-m^2) @ t~=m^2. $\endgroup$ More @Wikipedia
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