What determines the Lifetime of $Z$-Boson? What determines the lifetime of the Z Boson?  Is it it's mass? What else is involved? Is the coupling to Higgs involved?
 A: A $Z$ boson can decay to a variety of final states. About 70% of the time, it decays into a quark-antiquark pair, which proceed to create a jet of particles due to the strong interaction. About 20% of the time it decays into a neutrino-antineutrino pair. About 10% of the time it decays into a charged lepton-antilepton pair.
For each possible type of decay, one can use Feynman diagrams and Fermi’s Golden Rule to calculate the decay rate for that channel, which is the probability per unit time that the particle will decay in that way. The rate will depend on the mass of the $Z$, the masses of the final decay products and any intermediate particles, and the relevant coupling constants, the conceptually relevant ones being how strongly the $Z$ couples to quarks, neutrinos, and charged leptons due to the weak interaction. (Jet production from the quark and antiquark would involve the strong coupling constant for QCD.)
You add together the decay rates for the various channels, and take the inverse of that to get the $Z$ lifetime.
