I recently started studying Special Relativity for fun through reading the classic book Spacetime Physics. I came across a practice problem that I have difficult understanding:

An electron moving with some kinetic energy K collides with another electron to produce 2 gamma rays travelling at different angles with respect to the moving electron. Determine an expression for the energies as a function of the electron mass, energy, and angle of outgoing rays.

I'm not quite sure how to set up the conservation momentum equations to solve for this...?

  • $\begingroup$ actually you likely need conservation of the net momentum 4-vector. Presumably the second electron is at rest? $\endgroup$ – ZeroTheHero Mar 2 '17 at 3:26
  • $\begingroup$ Yes the second electron is at rest $\endgroup$ – stanfordude Mar 2 '17 at 3:31
  • $\begingroup$ I'm not too familiar with the mathematics involved with 4-momentum, but any help would be appreciated! $\endgroup$ – stanfordude Mar 2 '17 at 3:33
  • $\begingroup$ see here: en.m.wikipedia.org/wiki/Four-momentum or here: hyperphysics.phy-astr.gsu.edu/hbase/Relativ/vec4.html $\endgroup$ – ZeroTheHero Mar 2 '17 at 3:36
  • $\begingroup$ is it possible you are misquoting and it is an electron hitting a positron? Seems to me an undefined problem . $\endgroup$ – anna v Mar 2 '17 at 5:40

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