particleantiparticle

An antiparticle is the partner of a given particle that has the same mass but opposite additive quantum numbers. In many theories, every particle has a corresponding antiparticle, and together they can annihilate to release energy, typically in the form of photons or other bosons. The antiparticle’s charges, such as electric charge, baryon number, and lepton number, are opposite in sign to those of the particle. For neutral particles, the antiparticle may have opposite values only where applicable; some neutral particles are their own antiparticles.

Examples illustrate the concept: the electron has the positron as its antiparticle, the proton has the antiproton, and the muon has the antimuon. Neutrinos and antineutrinos are antiparticles of each other. Mesons are composed of a quark and an antiquark, while baryons and antibaryons consist of three quarks and three antiquarks, respectively. Some particles are self-conjugate, meaning they are identical to their antiparticles; photons, certain neutral mesons such as the neutral pion, and some gauge bosons are typically considered self-conjugate.

Processes involving antiparticles include pair production, where energy converts into a particle–antiparticle pair, and annihilation, where a particle and its antiparticle destroy each other, often producing photons or other particles. All fundamental interactions conserve the relevant quantum numbers, so charge, baryon number, lepton number, and other conserved quantities balance in creation and annihilation events.

Antiparticles play a central role in particle physics, cosmology, and experimental high-energy physics, contributing to tests of symmetries, the understanding of matter–antimatter asymmetry, and the study of fundamental forces.