# Homework Help: Pair-Production problems

1. Feb 21, 2007

### PhyzicsOfHockey

1. The problem statement, all variables and given/known data

How much photon energy would be required to produce a proton-antiproton pair? Give the answer in SI units.

2. Relevant equations

E^2=p^2c^2+m^2c^4
E=pc+pc
p=mc
E=2*m*c^2
3. The attempt at a solution

I seem to be confused I know the KE would be zero I also know this would not exist in real life but I need to find the min energy so KE of the photon pairs is 0. I am not sure if the equation has to do with the mass of a photon or the momentum of the photons. In either case I don't know what the mass of a photon would be. I read it was zero but can't figure out how to use this formula then.

2. Feb 21, 2007

### mjsd

ok... mass of a photon is zero... I think we all know that. But its momentum is not... we can agree on that too I think. Now, your key equation is
[tex]E^2=p^2 c^2+m^2 c^4[\tex]
where m here is the rest mass of your particle, p is its momentum and E is its total energy. To do your question: remember 4-momentum is conserved.....etc