What is Quark?

Quarks are not known to exist singly because of a physics theory called color confinement or simply confinement. This is a phenomenon in which strong interaction particles cannot be isolated singularly, so, cannot be directly observed. Quarks clump together to form groups called hadrons.

The two types of hadrons are the mesons(one quark, one antiquark) and the baryons (three quarks). The quarks in a group cannot be separated from their hadron, and this is why quarks can never be studied or observed in any way other than at the hadron level. Quarks come in six types.

For some reason physicists have decided to call them flavors. The six flavors of quarks are: up, down, top, bottom, charm, and strange. Up and down quarks are the most stable and have the lowest mass.

The other quarks have a heavier mass and decay into up and down quarks almost instantaneously. Based on that, you can see that the up and down quarks are the most common in the universe. As a matter of fact, most of the other quarks can only be produced in high energy collisions like those seen in cosmic rays or a particle accelerator.

Quarks have various natural properties, including electric charge, color charge, spin, and mass. Quarks are the only primary particles in the Standard Model of particle physics to experience all four of the fundamental forces: electromagnetism, gravitation, strong interaction, and weak interaction as well as the only known particles whose electric charges are not integer multiples of the electric charge carried by a proton or electron. For every quark flavor there is a corresponding type of antiparticle(antiquark) that differs from the quark only in that some of its properties have equal magnitude but opposite sign.

Quarks have many aspects in particle physics. Here is a link to a definition of a quark. Here on Universe Today we have several great articles related to the topic of quarks.

One is about the rare top quark, another is about all types of quarks, and the third one is about quark stars.