1. Introduction to the E391a

2. E391a Collaboration
High Energy Accelerator Research Organization, KEK, Japan
Joint 　Institute for Nuclear Research (Dubna), Russia
Department of Physics, Kyoto University, Japan
National Defense Academy of Japan, Japan
Department of Physics, National Taiwan University, Taiwan
Department of Physics, Osaka University, Japan
Department of Physics, Pusan National University, Korea
Research Center for Nuclear Physics, Osaka University, Japan
Faculty of Science and Engineering, Saga University, Japan
Department of Physics, University of Chicago, USA
Department of Physics, Yamagata University, Japan

3. KLgp0nn physics Flavor Changing Neutral Current
Direct CP violation (Ds =1)
　　　Im(Vtd) measurement
Very small theoretical ambiguity
　　　Only top loop in SM
　　　 clean and pure
Last frontier in K-decay
　　　challenging

4. Experimental situation - Current and future -

5. Mile stones Dec.1996: conditionally approved
Mar.1999: constructed the beam line
July 2001: approved
Oct. 2002: engineering run
Nov.2003: middle section (last vacuum 　　　　　　　　　　chamber) arrived
18 Feb. 2004: Started data taking

6. Detection Method Pencil Beam Pencil beam
Detector with complete veto system
4p coverage with thick calorimeter
Wide acceptance
Double decay chamber
Operation in high vacuum
High PT selection
Step by step approach
KEK-PS E391a
JPARC
Detector system

7. Detector system

8. Detector system (Cont.)

9. Detector Integration
Jan 22, 2004

10. Calibration using cosmic rays

11. Clearly reconstructed KL decay modes
KL  p0p0p0
KL  p0p0
6-g invariant mass (GeV/c2)
4-g invariant mass (GeV/c2)

12. JPARC

13. A-line plan at JPARC