Introduction to the E391a

E391a CollaborationHigh Energy Accelerator Research Organization, KEK, JapanJoint 　Institute for Nuclear Research (Dubna), RussiaDepartment of Physics, Kyoto University, JapanNational Defense Academy of Japan, JapanDepartment of Physics, National Taiwan University, TaiwanDepartment of Physics, Osaka University, JapanDepartment of Physics, Pusan National University, KoreaResearch Center for Nuclear Physics, Osaka University, JapanFaculty of Science and Engineering, Saga University, JapanDepartment of Physics, University of Chicago, USADepartment of Physics, Yamagata University, Japan

KL π0ννphysics

Flavor Changing Neutral Current

Direct CP violation (∆s =1)

　　　Im(Vtd) measurement

Very small theoretical ambiguity　　　Only top loop in SM　　　 clean and pure

Last frontier in K-decay　　　challenging

Experimental situation- Current and future -

Mile stones

Dec.1996: conditionally approvedMar.1999: constructed the beam lineJuly 2001: approvedOct. 2002: engineering runNov.2003: middle section (last vacuum 　　　　　　　　　　chamber) arrived18 Feb. 2004: Started data taking

Detection MethodPencil Beam

Pencil beamDetector with complete veto system

4π coverage with thick calorimeterWide acceptance Double decay chamberOperation in high vacuum

High PT selectionStep by step approach

KEK-PS E391a JPARC

Detector system

Detector system

Detector system (Cont.)

Detector Integration

Jan 22, 2004

Calibration using cosmic rays

Clearly reconstructed KL decay modes

KL π0π0KL π0π0π0

6-γ invariant mass (GeV/c2) 4-γ invariant mass (GeV/c2)

JPARC

http://j-parc.jp/

A-line plan at JPARC