From Compton scattering of photons on targets to inverse Compton scattering of electron and photon beams

We revisit the kinematics of Compton scattering (electron-photon interactions producing electrons and photons in the exit channel) covering the full range of energy/momenta distribution between the two colliding particles, with a dedicated view to statistical properties of secondary beams that are generated in beam-beam collisions. Starting from the Thomson inverse scattering, where electrons do not recoil and photons are backscattered to higher energies by a Lorentz boost effect (factor 4γ2), we analyze three transition points, separating four regions. These are in sequence, given by increasing the electron recoil (numbers are for transition points and letters for regions): (a) Thomson backscattering, (1) equal sharing of total energy in the exit channel between electron and photon, (b) deep recoil regime where the bandwidth/energy spread of the two interacting beams are exchanged in the exit channel, (2) electron is stopped, i.e., taken down at rest in the laboratory system by colliding with an incident photon of mc2/2 energy, (c) electron backscattering region, where incident electron is backscattered by the incident photon, and (3) symmetric scattering, when the incident particles carry equal and opposite momenta, so that in the exit channel they are backscattered with same energy/momenta, and (d) Compton scattering Arthur Compton, see A. J. Compton, A quantum theory of the scattering of X-rays by light elements, , 83 (1923), where photons carry an energy much larger than the colliding electron energy. For each region and/or transition point, we discuss the potential effects of interest in diverse areas, like generating monochromatic gamma-ray beams in deep recoil regions with spectral purification, or possible mechanisms of generation and propagation of very high energy photons in the cosmological domain. Published by the American Physical Society 2024