(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

two photons collide head-on and create an electron and an anti electron. The energy of photon 1 is given, but not for photon 2.

Find the velocity β of the systems rest frame (where the total momentum is zero.)

2. Relevant equations

β=v/c

γ=1/√1-β^2)

β=pc/E

3. The attempt at a solution

I have tried this every way I could think of, by adding the two momentum four vectors and using a lorentz transform on them, by using the formula for speed of the rest from β=pc/E, but no matter what, I always need the energy of the second photon. How do I get around needing this?!

Thank you for your help

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Photon-photon collision - electron-anti electron pair creation

**Physics Forums | Science Articles, Homework Help, Discussion**