Quarks in the Standard Model
Quarks and electrons are some of the elementary particles. A number of fundamental particles have been discovered in various experiments. So many, that researchers had to organize them, just like Mendeleev did with his periodic table. This is summarized in a theoretical model (concerning the electromagnetic, weak, and strong nuclear interactions) called the Standard Model. In particle physics, an elementary particle or fundamental particle is a particle whose substructure is unknown, thus it is unknown whether it is composed of other particles.
In the present Standard Model, there are six “flavors” of quarks, six quarks, just as there are six leptons based on a presumed symmetry in nature. The three quarks originally proposed and accepted were labeled u (up quark), d (down quark), s (strange quark). The other three quarks are called charmed, bottom, and top. They can successfully account for all known mesons and baryons. The most familiar baryons are the proton and neutron, which are each constructed from up and down quarks.