Today, we talk about electro-weak interaction because, since 1974, thanks to the works A. Salam, S. Weinberg and S. Glashow, the electromagnetic interaction and the weak interaction have been unified in the same description. According to this theory, there is a boson, called the photon, which transports the electromagnetic interaction: this is the light. For the transport of the weak interaction, 3 other bosons are needed: the W+, the W- and the Z. When a radioactive nucleus emits an electron (beta decay), it is in fact a neutron within the nucleus that transforms into a proton by emitting a W- which, soon after, decays into an electron anti-neutrino pair.
The weak interaction has very astonishing properties. Until now, this is the only known interaction where has been observed a violation of parity (P), which is the spatial symetry, and a violation of the symetry between particles and anti-particles (C).
In 1957, Mrs Wu and Misters Ambler, Hayward, Hobbes and Hudson of the National Bureau of Standards verified an hypothesis made some month earlier by two theoricists, T.D.Lee and C.N.Yang: the mirror image of a physical process where weak interaction is involved, does not exist in nature (P violation). The experiment seemed to prove also that the C symetry was violated.
J. Cronin and his team showed that,
in the decays of the particles called neutral kaons, not only the spatial symetry P was violated
but also, the combination CP was violated. This CP symetry breaking is very tiny but
could have created an initial asymetry between matter and antimatter
at the beginning of the universe. We would then all come from a very small overamount of matter
(1 billionth) thanks to the CP symetry violation in weak interaction!...
Until now, the CP violation had been observed only in neutral kaons decays. Since 2004, the BaBar experiment, using the Standford accelerator, has shown that CP is violtated also in the B mesons decays, and much more strongly.