⇒ A quark is one of the fundamental particles and combine to make protons and neutrons. The strong nuclear force is the force that connects quarks together to form the protons and neutrons.

⇒ Originally only the up, down and strange quarks were discovered, and the other 3 quarks (charm, bottom, and top quarks) were discovered later

⇒ The masses of the quarks in relation to a proton and an electron is seen here:

⇒ Most of a proton's mass is because of the energy involved in the interaction between quarks and gluons, which hold the quarks together through the strong nuclear force

• A gluon is is one of the exchange particles of the Standard Model. Gluons act between quarks holding them together, through the strong nuclear force that is carried by the gluon. Gluons have an extremely short range of action (approximately 10^-15m)

⇒ As the gluon interacts and exchanges between the quarks they come in and out of existence

• The energy required for a gluon to behave in this way is included within the mass of the proton or neutron itself (due to mass-energy equivalence, which states that mass is concentrated energy)

⇒ As seen above, the up and down quarks have the smallest masses.

⇒ Strange quarks are usually observed during high-energy interactions between cosmic rays and the Earth's atmosphere

⇒ The other quarks are only ever seen during extremely high-energy interactions, such as within a particle accelerator

⇒ The first time we saw a quark was through the deep-inelastic scattering in 1968

⇒ Deep-inelastic scattering is the process of firing electrons at protons at extremely high energies

• Elastic scattering is where two particles (such as protons) collide into each other and rebound with the same kinetic energy (i.e. no kinetic energy is lost)
• With inelastic scattering, kinetic energy is converted into other forms.
• When discovering the quark, the electrons that had been fired at the protons interacted with the quarks converting their kinetic energy (via E = mc²) into mass as a jet of new particles (i.e. pions)

⇒ If there had been no sub-structure to the protons, such inelastic scattering would not have occurred and kinetic energy would have been preserved

⇒ Also see our notes on:

• Introduction
• Fundamental Forces
• Feynman Diagrams
• Classification of Particles
• Conservation Laws