CP Violation

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Ever since Dirac predicted the existence of anti-particles in 1931, physicists have wondered how the reactions of particles relate to those of anti-particles.

In the beginning, it was imagined that if a particle were replaced by its anti-particle (which is called the C operation), the resulting anti-particle would obey the same laws of interaction. It was also thought that left-handed and right-handed particles (the designation refers to the relation of the spin of a particle to its direction of motion) obey the same interaction rules for much the same reasons. However, it was later found that this was not so, since weak interactions taking place via the exchange of the W vector bosons didn't conserve C symmetry. It was also observed that P is violated by weak decays. It was then conjectured that CP, which would involve replacing a left-handed particle with its right handed anti-particle, would be conserved. It is found that most interactions conserve CP-symmetry. Now, the mathematician Emmy Noether showed that for every symmetry, there is a corresponding conserved quantity. In our case, this quantity is called the CP-number, and can take the value of ±1. In 1964, Christenson, Cronin, Fitch and Turlay demonstrated that the long-lived neutral Kaon (KL) state, with CP number -1 decays into two pions, which was a state with CP number +1, about 3 times in 1000 decays.

Further, Andrei Sakharov showed in 1965, that, in order to explain the excess in the amount of matter over that of anti-matter in the universe, one of the three necessary criteria was the existence of CP-violation. However, the amount of CP violation that he predicted was in excess to the amount that had been observed. For this reason, we have searched, successfully, for CP violation. Decays of B mesons were chosen for this search, because they are highly asymmetric.