Alladi Ramakrishnan Hall

The 35+ years saga of direct CP violation

Amarjit Soni

Brookhaven National Laboratory

Calculation of the direct CP-violation parameter, epsilon', for K=> pi pi is a long standing challenge for theory. It is exceedingly difficult to calculate this reliably with accuracy as it entails large non-perturbative effects as has been widely recognized for past many decades due to the related challenge of the well-known "Delta I=1/2 puzzle" in these K-decays. Because of the realization that eps' is just about the most sensitive observable in our arsenal for detection of new physics, lattice methods for its computation were initiated some 35 years ago. After overcoming a huge number of obstacles first results demonstrating a reliable computational methodology was presented in 2015 indicating a possible tension with the Standard Model at about 2-sigma by our RBC-UKQCD Collaboration. In the past two and half years we have been working feverishly to improve this computation. To that end efforts are now in their final phase to improve statistics by a factor of about 6.5. A result is anticipated in the next few months. The methodology has provided answers to some long-standing puzzles. Those aspects as well as some important implications will be discussed.