How Many Generations?
The Z decays to the leptons and antileptons of each generation, as well as the quarks and antiquarks.
The more ways there are for the Z to decay, the easier it is for it to do so and the shorter its lifetime
Heisenberg’s uncertainty principle can be written
Coupled with E=Mc2, this says that the mass of the Z when it decays
is determined only up to a constant proportional to its lifetime