CP Violation in Kaon Decays (II)
Major progress has been made in kaon physics in the past 50 years. The number of KL->pi+pi- events has increased by 6 orders of magnitude, and the observed CP violation was experimentally proven to be caused by a complex phase in the CKM matrix. Recent kaon experiments are now searching for new physics beyond the standard model with the K->pi nu nu-bar decays. The branching ratio of K->pi nu nu-bar decays are 7-8 orders of magnitude smaller than the branching ratio of KL->pi+ pi-. 
This paper reviews the progress of kaon experiments in the US and Japan, and how the 6-7 orders of magnitude improvements were possible in the past 50 years.