decay rate Zo boson

[Rothiemurchus]

The decay rate of the Zo boson depends on the number of kinds of
neutrino.Does each kind of neutrino contribute to the decay rate equally?
Are there more electron neutrinos than muon or tau neutrinos?

[zefram_c]

Each neutrino type contributes equally - the coupling of the Z to neutrinos is the same for all flavors, and the neutrino masses are totally negligible.
Are there more electron neutrinos than muon or tau neutrinos? In what sense? In the universe? As produced in the Sun's core? As produced in Z decays? Clarify.

[Rothiemurchus]

In open space and in z decays.

[zefram_c]

In Z decays: all neutrinos are equally likely to be produced. This is likely NOT tested directly, since we have a hard time producing Z's in the first place, and it's just too much to hope to detect and identify the produced neutrinos. What we do know is that the Z decays invisibly (ie. no observed end products) with some probability (~20%), which that is consistent with three species of neutrinos produced equally likely. (The theory is of course much tighter / well tested than this)

In open space: a very good question! All neutrinos produced *now* in stars are electron neutrinos, but with the advent of neutrino oscillations, that means that in free space, the composition is different. About a third of the solar neutrinos reaching Earth are electron neutrinos.

There is also an expectation that there is a "neutrino background" of origin similar to that of the CMB. Since I know very little astrophysics, I suggest asking in that forum about this background if you're interested.