Antimatter

Antimatter is a challenge to physicists. P.Dirac introduced the concept of antimatter in 1932 and since then the counterpart in the antimatter world of most particles has been discovered. The likeness of both worlds was explained by the fact that particles and anti-particles must comply with CPT invariance. In 1956 a Chinese team showed that kaons break the P-symmetry. In order to save the CPT theorem it was assumed that the C-symmetry was also broken in kaon system. It was a short-lived relief and in 1964 an American team discovered processes that did not comply with the CP-symmetry. In 1964 the Russian physicist A. Sakharov stated that the CP-breaking favours the disappearance of antimatter. This idea implies that the CP-symmetry breaking should occur in lot of processes, so different research programs have been launched to study CP and T invariance. The experiments NA48, BABAR and CP-LEAR are briefly described. Whenever antimatter meets matter, a burst of energy is released and then can be detected, so our galaxy did not contain any antimatter. As for the rest of the universe, if antimatter exists it must be in places out of reach of our instruments. (A.C.)