CP violation: Progress and prospects

From the first days of the discovery of CP-violation, there was speculation that the effect was caused by a long range field which predicted that the K/sub L/→ππ decay rate depended on laboratory momentum. Experiments at energies < 10 Gev have revealed no energy dependence. With ε' = O, which is consistent with the data, all the CP violating phenomena observed can be accounted for by one number which is the length of ε. It is clear that a single number can be accommodated by a large number of theories. If new experimental work can uncover a second independent parameter which describes CP violation. The knowledge will be doubled, and there will be a better chance of understanding its origin. It is for this reason that the author's group at Chicago in 1979 began to consider measurements of vertical bar eta/sub oo//eta/sub +-/vertical bar/sup 2/. The neutral decay modes were poorly known and the precision on the determination of the second parameter ε' could be significantly improved. Shortly thereafter the author's work got an important boost from the theoretical side, as well as being joined by other proposals. Within the standard model, other authors pointed out that with three generations of quarks and leptons a CP violating phase angle could appear in the weak mixing matrix. Then in terms of the four angles (three Cabbibo-like mixing angles and the phase angle δ) the values of ε' and ε' could be computed. The great difficulty in this program is the ''theoretical engineering'' required to go from the weak interactions of quarks to the weak interactions of hadrons