Particle Families and Leptons

Particle Families and Leptons

The kinetic energy of colliding particles in accelerators can be converted into mass to produce exotic short-lived particles. The latter soon decay into more familiar stable particles such as the proton. Studies of the properties of these particles have enabled physicists to find patterns linking the properties and to use these patterns to predict the existence of yet more particles.

There are two main families of particle, the leptons and the hadrons.

These are the lightest particles. Their name is derived from Greek: Lepton is small.

There are 3 types of lepton: the electron, muon and tau. In addition, each of these particles has an associated neutrino, and corresponding antiparticle, making a total of 12 family members. Leptons are truly fundamental.

They experience gravitational, electromagnetic and the weak nuclear forces but not the strong nuclear force.

Lepton Particle Symbol Antiparticle Symbol
electron e- e+
electron neutrino νe Copyright S-cool
muon µ- µ+
muon neutrino νµ Copyright S-cool
tau τ- τ+
tau neutrino ντ Copyright S-cool

These last four are highlighted because they are unstable. They are created in high-energy collisions but soon decay to stable particles.

The 3 rows in the table represent 3 'generations' of matter. The particles in one generation have the same properties as the corresponding particles in the other generations but successive generations have more mass. Only the first generation makes up the matter we observe in the universe.

Leptons are assigned a Lepton number (L). L = 1 for leptons and L = -1 for antileptons.