Lepton Collisions

When a lepton meets its antiparticle they can annihilate. In electron-positron annihilation the mass of the two particles is converted into energy, and the particles created must obey the conservation laws.At low collision energies the electron and positron produce two gamma photons travelling in opposite directions, so that momentum is conserved. Each photon has a minimum energy equal to the rest energy of an electron, 0.511 MeV.At higher collision energies the energy can create new particle-antiparticle pairs instead, such as a muon and an antimuon, or a quark and an antiquark. The pair is produced through a virtual photon or a Z boson. The more energy available, the more massive the particles that can be created, since E = mc².Quarks cannot exist on their own, so a quark and antiquark produced in this way immediately combine with other quarks to form hadrons, such as mesons and baryons. For example, a bottom quark and its antiquark can form B mesons.Charge, baryon number and lepton number are all conserved. An electron and a positron have a total charge of 0 and a total lepton number of 0, so the products must also have a total charge and lepton number of 0.