This page summarizes the known elementary particles. Just a handy reference so that I no longer have to Google for it.
Matter Particles
Matter particles are characterized by the fact that they are all fermions, with ±½ spin. (Neutrinos come in only one spin state; the opposite spin state belongs to the antineutrino.) In addition to their spin, these particles have mass, electric charge and "color charge". All matter particles have "proper" antiparticles, with an opposite charge.
| Family | neutrinos |
quarks |
(confined) | charged leptons | ||||
|---|---|---|---|---|---|---|---|---|
|
Charge: |
0 | –1/3 | 2/3 | –1 | ||||
| e | νe | m < 2 eV | qd | m = 4.1–5.8 MeV | qu | m = 1.7–3.3 MeV | e | m = 0.511 MeV |
| μ | νμ | m < 2 eV | qs | m = 101+29–21 MeV | qc | m = 1.27+0.07–0.09 GeV | μ | m = 105.66 MeV |
| τ | ντ | 0.04 < m < 2 eV | qb | m = 4.19+0.18–0.06 GeV | qt | m = 172.0±1.6 GeV | τ | m = 1776.82±0.16 MeV |
Free quarks do not exist. Any attempt to isolate quarks requires so much energy that it is sufficient to produce additional quarks, and therefore quarks remain "confined" in composite particles.
Matter particles interact with each other through four forces. All particles interact gravitationally. All particles interact through the weak interaction. Only charged particles (i.e., quarks, electrons, muons, and tau particles) interact electromagnetically. Lastly, only particles that have a color charge, quarks that is, participate in the strong interaction.
Interactions are mediated by another family of particles.
"Interaction" Particles
In addition to particles that comprise matter, there exist particles that "carry force". All known such particles are spin-1 particles. The photon and the Z-boson are their own antiparticles; the W+ and W– mesons are antiparticles of each other. As for the gluons, see the link below to an excellent explanation by John Baez.
| Interaction | Particle(s) | |
|---|---|---|
| Electromagnetism | γ |
m = 0 |
| Weak interaction | W± | m = 80.399±0.023 GeV |
| Z |
m = 91.1876±0.0021 GeV | |
| Strong interaction | 8 gluons | m = 0? |
Like quarks, gluons do not exist freely. Some people do, however, speculate about the existence of particles composed only of gluons, so-called "glueballs".
This concludes the list of known particles. All other "elementary" particles are either not elementary but are composites, or they are not experimentally observed.
Hypothetical Particles
In addition to the known set of particles, many physicist accept as fact the existence of the graviton (a hypothetical spin-2 particle that mediates the gravitational interaction) and the Higgs-boson (a spin-0 particle that is behind the hidden symmetries of some unification theories; current results suggest that if it exists, its mass must be greater than 114.4 GeV and less than 185 GeV). Other particles that may exist include the gravitino (a "light", spin-1 version of the graviton), and various supersymmetric counterparts of known particles, like the selectron (a spin-1 counterpart of the electron) or the sphoton (a spin-½ version of the photon.) It is important to note, however, that these particles are not known to exist: their existence is conjectured on the basis of various (sometimes beautiful, sometimes ugly, but all unproven) theories.
