How do you distinguish between neutrinos of different types?

[alemsalem]

since we don't know its mass,, is it by looking at the lepton by products?

 

[ofirg]

is it by looking at the lepton by products?

Exactly.

When measuring a $\nu$, we don't have the sensitivity required to idendify the mass eigenstate.

we measure the flavor, by identifying the flavor of the lepton produced.

See for example opera's measurement of tau neutrinos in a muon neutrino dominated beam

by identifying the tau decay http://arxiv.org/pdf/1006.1623v1.pdf