Symmetries and symmetry breaking remain one of the most powerful theoretical and experimental tools for exploring our understanding of the fundamental forces of nature. The electroweak interaction is known to violate parity (P) and charge conjugation (C), two basic discrete symmetries that are conserved by all other forces. Surprisingly, in 1964, it also was found to violate CP at the 0.2% level in decays of neutral kaon states. Since that time, no evidence for CP violation outside the kaon system has been observed, although we now know that the Standard Model with three quark families incorporates a natural mechanism for creating a rich spectrum of CP violation phenomenon.
In particular, the interference between amplitudes for mixing and decay in the neutral B system should produce large and measurable time-dependent effects, most notably in decays to CP eigenstates such as J/psi-K0S or other charmonium modes. Intriguingly, the cosmological matter-antimatter asymmetry observed in the universe cannot be explained by the level of CP violation built into the electroweak interaction.
Over the last 10 years, two asymmetric energy e+e- storage rings, known as B Factories, have been built with the express purpose of making definitive tests of the Standard Model expectations for CP violation in the B system. One of these, the BABAR experiment, began operation at the SLAC PEP-II B Factory in June 1999 and has already recorded 100 million B-anti-B events. Recently, this sample has been used to demonstrate the first significant example of CP violation outside the neutral kaon system. This talk will examine the ideas and experimental methods behind this demonstration of CP violation, as we continue to explore both Standard Model expectations and look for the additional effects of new physics.