mass of the particles produced.This resulted in a wide variety of new particles. Initially there was difficulty categorising all these new particles so they became known as the ‘particle zoo’.
Over time physicists realised that matter can be categorised according to whether it is made from particles that are subject to the strong nuclear force or not. The family of particles that do not experience the strong nuclear force are called leptons, those that do are called hadrons, and these are further subdivided into baryons and mesons.
Leptons
LEPTONS Leptons are indivisible point objects that are not subject to the strong force.
‘Lepton’ is the Greek word for ‘light’. Examples include electrons, positrons and neutrinos.
Leptons can be categorised into ‘generations’, each generation being heavier than the previous.Heavier particles require more energy to produce them and are also less stable. They decay into lighter particles after very short periods of time.
There are six leptons, along with their six corresponding antiparticles. They are the electron (e), muon () and tau (), their neutrinos and all their antiparticles.The table below shows all the leptons along with all the information we need to know about them.
LEPTONS
Particle name
Generation 1 Electron
Electron neutrino
Generation 2 Generation 3 Muon
Muon neutrino Tau
Tau neutrino Table 23.2: Description of the six leptons Hadrons
HADRONS Hadrons are subatomic particles that experience all the fundamental forces, includ- ing the strong nuclear force.
