| DATE: |
2008-01-16 16:00 - 17:00 |
| PLACE: |
Room 345, Building 4 |
| TITLE: |
New Result from KEK-PS E391a on the search for the decay KL->pi0 nu nubar |
| CONTACT: |
Takeshi Komatsubara (takeshi.komatsubara kek.jp) |
| SPEAKER: |
Toshi Sumida (Kyoto University) |
| LANGUAGE: |
English |
| ABSTRACT: |
The rare decay KL->pi0 nu nubar is a Flavor Changing Neutral Current process from strange to down quarks and its observation is a new evidence for direct CP violation. The amplitude is proportional to the imaginary part of the CKM matrix elements. The branching ratio is predicted to be (2.49¡Þ0.39)x10^(-11), and its irreducible theoretical uncertainty in the standard model (SM) is only 1-2%.
KEK-PS E391a is the first dedicated experiment to this decay mode. The beam line is very narrow (2mrad half cone angle) to set the constraint to pi0 kinematics. The detector hermetically covers the decay region to reduce the backgrounds from other decay modes which have extra particles. The current experimental upper limit is set to be Br < 2.1x10^(-7) by the first result in E391a.
The second run period (RunII), with several crucial upgrades in the detector, was carried out from February to April in 2005. We report the result using the full data set taken in RunII. (arXiv: 0712.4164) |
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