| Definition: | for a given kind of particle, that particle for which each characteristic that can assume two values has the complementary value, while the remaining characteristics are the same NOTE 1 The concept of antiparticle applies to both elementary particles, e.g. positron as antiparticle of electron, and compound particles, such as proton, neutron and atom. NOTE 2 A particle and its antiparticle have in particular the same rest mass, the same spin quantum number, and opposite electric charges. Particle and antiparticle may be identical, for example photons. NOTE 3 A particle and its antiparticle may interact, resulting in two photons. This process is usually called annihilation. NOTE 4 An antiparticle is generally denoted by the same symbol as the corresponding particle but overlined, and its name is generally the name of the particle with the prefix anti, e.g. antiproton corresponding to proton p, antihydrogen atom corresponding to hydrogen atom.
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