It is now understood as a result of the quark model.

In a strong interaction, a strong force particle, such as this one, interacts with a colored quark, such as this green one, to give a quark with a different color charge this red one.

During the quark epoch, the electroweak force split into the electromagnetic and weak forces.

There are multiple processes that can lead to the production of a top quark.

The largest effect from the top quark mass was on the T parameter and by 1994 the precision of these indirect measurements had led to a prediction of the top quark mass to be between and .

They increase in value at lower energy scales, at which the quark masses are generated by the Higgs.

This mixing is parameterized by the PMNS matrix, which is the neutrino analogue of the CKM quark mixing matrix.

Values in red have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements.

Mass Despite being extremely common, the bare mass of the down quark is not well determined, but probably lies between 4.5 and 5.3.

The value of the fixed point is fairly precisely determined in the Standard Model, leading to a top quark mass of 230 GeV.

So when two up quarks and a down quark are combined to make a proton, it has a total electric charge of plus one.

It, along with the strange quark is part of the second generation of matter, and has an electric charge of e and a bare mass of .

It was in fact not long until a fifth quark, the bottom, was discovered by the E288 experiment team, led by Leon Lederman at Fermilab in 1977.

Maskawa and Kobayashi's theory required that there be at least three generations of quarks, a prediction that was confirmed experimentally four years later by the discovery of the bottom quark.

Baryons (three quarks) have a baryon number of 1, mesons (one quark, one antiquark) have a baryon number of 0, and antibaryons (three antiquarks) have a baryon number of 1.

These effects become much larger for higher values of the top mass and therefore could indirectly see the top quark even if it could not be directly produced in any experiment at the time.

Heavier quarks can only be created in high energy collisions (such as in those involving cosmic rays), and decay quickly however, they are thought to have been present during the first fractions of a second after the Big Bang, when the universe was in an extremely hot and dense phase (the quark epoch).