Speaker
Hiroaki Watanabe
(KEK)
Description
The neutral-kaon decay KL -> pi0 nu anti-nu is a direct CP-violating process caused by a flavor-changing neutral current, and the branching ratio is predicted to be (2.49+-0.39) * 10^(-11) in the Standard Model. The rare decay is one of the processes expected to have a significant impact on new physics searches. The E391a experiment at the KEK 12-GeV proton synchrotron was the first dedicated search for KL -> pi0 nu anti-nu. The final results, which have just been published in Phys.Rev.D81, 072004 (2010), are reported in this contribution. Combining the data sets in February-April 2005 (Run-2) and October-December 2005 (Run-3), the single event sensitivity was 1.11 * 10^(-8) and no events were observed in the signal region. The upper limit on the branching ratio was set to be 2.6 * 10^(-8) at the 90% confidence level. The E391a experiment as a whole has improved the limit from the experiments (FNAL-KTeV, ...) by a factor of 20.
Primary author
Prof.
Takeshi Komatsubara
(KEK)
