[TALK/CM-06001] Let's Talk --- Scattering

In a scattering process a beam of particles, or of waves, is incident on a target. In most general situations, the final state may consist of 'anything', subject only to conservation laws such as energy, momentum etc..

Study of scattering processes is one of the important methods for studying the 'unknown'. There are many experiments where important discoveries were made through scattering. The existence of nucleus was first revealed in the famous Rutherford experiments of $\alpha$ particle from gold foil. The Franck-Hertz experiment on electron scattering confirmed the discrete nature of energy levels of atoms. X-ray scattering from crystals and showed the crystal structure. The deep inelastic scattering of electrons led to the discovery of quarks inside hadrons. These are a few important examples; there are many more examples where study of scattering played an important role in new important discoveries.

An important case of scattering is elastic scattering. An elastic scattering is a two body process process \[ a + b \longrightarrow a + b \] such that

1. no new particles are produced,
2. the target does not capture particles from the incident beam
3. no new particles are produced
4. there is no exchange of energy between the particles involved; their internal energies remain unchanged. For example, in electron atom scattering the final atom remains in the same state as the initial state.

All scattering processes, where at least one of the above conditions is not satisfied. are called inelastic scattering.