# (Special relativity)

Hi everyone,

I am stuck at a really straight-forward problem about SR:

In a beam of antineutrinos, it is proposed to search for tau anti-neutrino via their interactions on protons in a stationary target to produce anti-tau particles.

(a) Calculate the minimum energy of the tau anti-neutrino which would permit anti-tau production; (I have done this far, by using the fact that 4-momentum squared is frame invariant)

(b) What is the energy of the produced anti-tau when tau anti-neutrino has this threshold energy?

I just wonder what the strategy is, or what would be the most clever and neat way to do it.

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