Electron–positron annihilation
Electron–positron annihilation occurs when an electron () and a positron (, the electron's antiparticle) collide. At low energies, the result of the collision is the annihilation of the electron and positron, and the creation of energetic photons: + → + At high energies, other particles, such as B mesons or the W and Z bosons, can be created. All processes must satisfy a number of conservation laws, including: Conservation of electric charge. The net charge before and after is zero. Conservation of linear momentum and total energy. This forbids the creation of a single photon. However, in quantum field theory this process is allowed; see examples of annihilation. Conservation of angular momentum. Conservation of total (i.e. net) lepton number, which is the number of leptons (such as the electron) minus the number of antileptons (such as the positron); this can be described as a conservation of (net) matter law. As with any two charged objects, electrons and positrons may also interact with each other without annihilating, in general by elastic scattering. Low-energy case There are only a very limited set of possibilities for the final state. The most probable is the creation of two or more gamma photons. Conservation of