TABLE OF CONTENTS As we saw in the previous chapter, weak interactions violate, separately, both the C and P symmetries. Nevertheless, it was thought until the early 1960s that the combined operation of CP might hold for all interactions. Because the CP transformation takes a physical particle state to a physical antiparticle state, as shown in the example of Eq. (11.62), invariance under CP is equivalent to having a particle-antiparticle symmetry in nature. However, the universe is known to be dominated by matter, with essentially no antimatter present, which is tantamount to saying that there is a definite particle-antiparticle asymmetry in the universe. This would suggest that CP may not be a symmetry of all the fundamental interactions, and, in fact, as we will describe below, there are processes in which the combined operation of CP is violated. In this chapter we discuss the violation of CP in weak interactions. It should be recognized that, if CPT is a symmetry of all physical systems, then a violation of CP automatically implies that T must also be violated. CP violation therefore implies that there are microscopic (subatomic) processes for which time has a unique direction of flow.
We have already discussed the ?- ? puzzle, where we concluded that the decays of the ? + ( ? ? ) and the ? + ( ? ? ) can be identified as two decay...
