The subatomic zoo

Fundamental particles can be divided into three categories, quarks, leptons and gauge bosons. Quarks are the constituents of baryons, like protons and neutrons. Protons and neutrons are not fundamental since they are comprised of other particles.

All quarks carry a baryon number of 1/3. Therefore conservaton of baryon number can be stated as conservation of quark number. Quarks also come in three colors (red, green and blue). The colors are just names and don't refer to real color. It turns out that on length scales greater than 1.0 E-15 m only colorless objects exist in nature. For instance, a proton which is comprised of two up quarks and one down quark must have one quark of each color to remain colorless.

Aside from the electron, there are two other species of negatively charged leptons. There are also three corresponding neutrinos. All the leptons in the table have a lepton number of -1.

The gauge bosons mediate the forces between the quarks and between each other. For instance the photon corresponds to the electromagnetic field, which is created by charged particles and then affects other charged particles. The W and Z bosons mediate the weak interaction, while the gluons mediate the interaction of quantum chromodynamics (QCD) which is the interaction between colored objects that binds quarks together to make protons and neutrons.

Fermions (all spin 1/2)

  color charge(e) mass(MeV/c2)
up yes, 3 2/3 4
down yes, 3 -1/3 7
strange yes, 3 -1/3 150
charm yes, 3 2/3 1500
bottom yes, 3 -1/3 4700
top yes, 3 2/3 1.7 E5
  color charge mass(MeV/c2)
e no -1 0.511
ne no 0 0
m no -1 105
nm no 0 0
t no -1 1784
nt no 0 0

Gauge bosons (all spin 1)

  color charge(e) mass(MeV/c2)
photon no 0 0
W+ no 1 8.1 E4
Z no 0 9.1 E4
W- no -1 8.1 E4
gluons yes, 8 0 0

Examples     Particle physics' index