In part I, we discussed the fundamental forces in physics and the dual nature of particles and fields. We also talked about how the elementary particles of the Standard Model are divided into fermions and bosons. In part II, we went over the essential characteristics of the elementary fermion family. In part III, we covered the elementary bosons, and today we take a look at Hadrons, which are the particles in which quarks are confined. As before, we’re chopping these up into very short mini-lessons in order to combat the problem of people being too busy to read something like this if we’d crammed it all into one long lesson.
Hadrons, which are composed of quarks, are subdivided into baryons, and mesons (Young and Freedman 1523). Baryons are comprised of three quarks each and include, for example, the proton and the neutron (Young and Freedman 1523). So, the nuclei of atoms are comprised of baryons, and since the matter with which we interact on a daily basis is comprised of atoms, (as most of you are no doubt well-aware), baryons thus play a significant role in our lives.
Since they have half-integer spin quantum numbers, individual baryons are also Fermions. Mesons, such as pions and kaons, consist of one quark and one anti-quark each, of which there are several combinations (Young and Freedman 1523). In fact, not only do anti-quarks exist, but every matter particle in the Standard Model has a corresponding anti-matter particle characterized by the opposite sign of its internal quantum numbers but the same spin and mass; particles and their anti-particles can mutually annihilate and in the process convert their mass to energy (Martin 182).
The properties of “spin” as well as the existence of anti-matter both emerged when physicist Paul Dirac successfully combined quantum mechanics with Einstein’s special theory of relativity in 1927 (Baggott 38).Additionally, since mesons also have integer spin quantum numbers, that makes them, by definition, bosons.
The quarks that comprise Hadrons are bound together by the nuclear strong force, or the nuclear strong interaction, which, as we mentioned in part II, is mediated by “colored” gluons (of which there are 8 types). Color in this context does not refer to color in the visual sense, but is rather just a name physicists have given to another property of gluons. For this reason, the strong interaction is sometimes referred to as the “color force,” which you can read more about here.
In the next installment, we’ll discuss the Higgs Boson, and I’ll provide some references along with a glossary.