Baryons (from the Greek barys — heavy), a group of “heavy” elementary particles with half-integer spin and a mass not less than the mass of the proton. The baryons include the proton and the neutron, the hyperons, some of the resonances and of the “charmed” particles and, possibly, some others. The name “baryon” comes from the mass of the lightest of them — the proton is 1836 times heavier than the electron. There is only one stable baryon — the proton; the other baryons are unstable and through successive decays turn into the proton and light particles. (A neutron in the free state is an unstable particle — yet in the bound state inside stable atomic nuclei it is stable.) Baryons take part in all the known fundamental interactions: the strong, the electromagnetic, the weak and the gravitational. In every process yet observed the law of conservation of the number of baryons holds: the difference between the number of baryons and the number of antibaryons remains unchanged. This law can be given a form that recalls the law of conservation of electric charge if a specific baryon charge is ascribed to the baryon. The law of conservation of the number of baryons then takes the form of a law of conservation of baryon charge. One of the ways this law shows itself is that the creation of an antibaryon is necessarily accompanied by the creation of a further baryon. There are, however, theoretical considerations according to which the law of conservation of the number of baryons is only approximate (see Baryon charge).