APPENDIX A - The standard model of the physics of elementary particles

Summary

Matter is made up of two kinds of elementary particle, quarks and leptons, each having six varieties divided into two groups of three:

Quarks

up, charmed, top (all three have charge +2/3;)

down, strange, bottom (all three have charge -1/3;)

Leptons

electron, muon, tauon (all three have charge -1)

neutrino_e, neutrino_μ, neutrino_τ (all three have charge 0).

The three neutrinos are not interchangeable; they are distinguished by indices

Usual matter

matter we are familiar with is made up only of:

the up quark, the down quark, and the electron; in particular:

the proton is made up of three quarks: up, up, down (charge +1),

the neutron is made up of three quarks: up, down, down (charge 0).

Mesons

elusive particles made of 1 quark and 1 antiquark; the 6 types of quarks make 36 types of mesons.

Forces of nature

Four types of force of different symmetries occur among matter particles; these forces are carried by particles of a new kind:

1. (1) electromagnetism, carried by the photon (light, X-rays, γ rays, etc.)

2. (2) the weak force is carried by three particles: W⁺, W^- and Z⁰

3. (3) the strong force is carried by eight ‘colors’ of gluons

4. (4) gravitation is carried by the graviton

The standard model unifies electromagnetism and the weak force, as if the three particles W⁺, W^- and Z⁰ were actually heavy photons.

The existence of the top quark had been predicted for a score of years; it was finally observed in 1994, completing the list of elementary particles.