Initial and final state radiation

In particle physics, initial and final state radiation refers to certain kinds of radiative emissions that are not due to particle annihilation. It is important in experimental and theoretical studies of interactions at particle colliders. In particle physics, initial and final state radiation refers to certain kinds of radiative emissions that are not due to particle annihilation. It is important in experimental and theoretical studies of interactions at particle colliders. Particle accelerators and colliders produce collisions (interactions) of particles (like the electron or the proton). In the terminology of the quantum state, the colliding particles form the Initial State. In the collision, particles can be annihilated or/and exchanged, producing possibly different sets of particles, the Final States. The Initial and Final States of the interaction relate through the so-called scattering matrix (S-matrix). The probability amplitude for a transition of a quantum system from the initial state having state vector | i ⟩ {displaystyle |i angle } to the final state vector | f ⟩ {displaystyle |f angle } is given by the scattering matrix element where S {displaystyle S} is the S-matrix. The electron-positron annihilation interaction: e + e − → 2 γ {displaystyle e^{+}e^{-} o 2gamma }