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Deep Inelastic Scattering
If we can use electrons to "see" protons inside the nucleus, can we also use them to see inside protons?
The direct evidence for the existence of quarks inside the proton is provided by deep inelastic scattering. The idea is to accelerate electrons to very high energies, then allow them to interact with a stationary proton, and investigate what happens. But why is this called deep inelastic scattering?
At high energies, the wavelengths associated with the electrons are much smaller than the size of a proton. Hence the electrons can probe distances that are small compared with the proton - that is, DEEP within the proton. However, the high energies tend to disrupt the proton, so that it produces several new particles (hadrons). This means the scattering is INELASTIC because the target has been changed in the process.
Deep inelastic scattering may be viewed in two ways: as inelastic scattering off a proton because it has constituents inside, or as elastic scattering from one of the constituents inside (ignoring the whole proton and other constituents). We are able to say that the constituents appear to be point-like and so can be considered to be fundamental particles.