antifermions

Antifermions are the antiparticles of fermions—the fundamental particles with half-integer spin. For every fermion f, there exists a corresponding antifermion f̄ with the same mass and spin magnitude but opposite charges and other additive quantum numbers. Antifermions obey Fermi-Dirac statistics just like their matter counterparts. In quantum field theory, the relationship between a particle and its antiparticle is governed by CPT symmetry, which relates a particle to its antiparticle with reversed spatial coordinates and spin.

Examples include the electron and the positron, up and anti-up quark, down and anti-down quark, and the antiproton and antineutron. Mass is identical in each pair, while electric charge and other additive quantum numbers (such as baryon number, lepton number, or flavor quantum numbers) have opposite values. Neutrinos are peculiar: in many theories they are Dirac fermions with distinct antineutrinos, but some models allow neutrinos to be Majorana fermions, in which case the particle could be its own antiparticle.

Antifermions can be created in particle-antiparticle pairs in high-energy processes, such as electron-positron annihilation or quark-antiquark production in colliders. They can annihilate with their matter counterparts, typically releasing energy in the form of photons or other gauge bosons, conserving all relevant quantum numbers.

In the Standard Model, the existence of antifermions is essential to conserve baryon and lepton numbers in interactions to date. Studying antimatter, including antihydrogen and heavier antibaryons, provides tests of fundamental symmetries and interactions in particle physics.