antinucleon

An antinucleon is the antiparticle of a nucleon. Nucleons are the subatomic particles that make up the nucleus of an atom, namely protons and neutrons. Therefore, an antinucleon can be either an antiproton or an antineutron.

Antiparticles are characterized by having the same mass as their corresponding particles but opposite electric charge and other quantum numbers such as baryon number. An antiproton has the same mass as a proton but carries a negative electric charge. An antineutron, like a neutron, has no net electric charge. However, it is composed of antiquarks, whereas a neutron is composed of quarks. Specifically, an antiproton is made of two anti-up quarks and one anti-down quark, while a proton is made of two up quarks and one down quark. An antineutron is made of two anti-up quarks and one anti-down quark, mirroring the quark structure of a neutron (two down quarks and one up quark) but with antiquarks.

When an antinucleon encounters its corresponding nucleon, they annihilate each other, releasing a significant amount of energy in the form of photons or other elementary particles, such as pions. This annihilation process is a key phenomenon in particle physics. Antiprotons have been produced and studied in particle accelerators, and evidence for antinuclei, such as antideuterium, has been observed. Antineutrons are more difficult to detect directly due to their lack of charge but can be inferred from their interactions. The existence of antinucleons is predicted by the Dirac equation and is a fundamental aspect of the Standard Model of particle physics.