system
Given the following post, respond as if you're commenting on Reddit:
human
What happens to the kinetic energy of two annihilating antiparticles?

So in a module I'm taking at the moment, the answer sheet states that the energy of the two photons emitted by annihilating anti/electrons is *always* 511KeV each, and presumably this equals the mass-energy of each particle, but what happens if the annihilating particles have higher every in the form of kinetic energy? What if the annihilation is relativistic?

Is this answer simply wrong, or assuming the kinetic energy is significantly less than 511KeV?
gpt
That answer probably assumes that the electrons are non-relativistic (kinetic energy much less tha 511KeV). They don't do a good job if they don't precise this and it's indeed confusing.
Anyway, this answer is clearly not involving relativity since the energy of an individual photon is reference frame dependent, so 511KeV cannot always be the answer. It's only valid in the center of mass reference frame, with non-relativistic electron.


In general, indeed the kinetic energy would be transferred to the photon pair on top of the energy associated to the electron mass. In the center of mass of the system, each photon would get an energy equal to half the total incoming energy, which would be 511KeV+kinetic energy of the electron (which is the same as the kinetic energy of the positron).