Nuclear and Particle Physics: Quarks

Quarks and Their Properties

Quarks are elementary particles that combine to form hadrons such as protons and neutrons.
There are six flavours of quarks: up, down, charm, strange, top, and bottom.
Each quark has an antiquark with opposite charge.
Quarks have fractional electric charge: up, charm and top quarks have a charge of +2/3, while down, strange and bottom quarks have a charge of -1/3.
Quarks possess a type of charge called colour charge which contributes to the strong interaction, not to be confused with visual colours.

Quark Confinement and Colour Charge

Quarks are always found in combinations that form colour-neutral particles, a concept known as quark confinement.
Quarks are never observed in isolation due to the strong nuclear force, which acts like a rubber band, pulling quarks back together when they try to separate.
The exchange particle for the strong nuclear force is the gluon.

Quark Composition in Particles

Changes In Quark Composition

Quarks can change their type through a process known as a quark transition.
Quark transitions are mediated by weak nuclear force, which can change a down quark to an up quark (or vice versa).
These transitions are involved in forms of particle decay, such as beta decay.

Quark-antiquark Pairs and Mesons

When a quark encounters its corresponding antiquark, it can produce a meson. For example, a down quark and an antidown quark can produce a pion.

Baryons and Mesons

Baryons are particles made up of three quarks, such as protons and neutrons.
Mesons are particles that consist of a quark-antiquark pair. They involve the exchange of virtual particles (pions) between protons and neutrons in the atomic nucleus.