1. Measurement of KL  p0nn decay
G.Y.Lim
IPNS,KEK

2. Why KL→p0nn ? Flavor Changing Neutral Current
Br(KL g p o n n ) = 6 k1 ・Im(VtdVts)2X2(xt)
　 = 1.94・10-10h2A4X2
Strong Interaction : Factorized by Ke3 Decay *
Negligible Charm contribution
Very Small Theoretical Uncertainty

3. In JHF era h r Unitarity Triangle vertices Beyond Standard Models
K+  p+nn
KL  p0nn
E391a
DMBd/DMBs
ACP(BJ/YKS) r
G. Buchalla hep-ph/
L.Littenberg HEPAP(2001)

4. Search for the decay KL  p0nn po  gg po  e+e- g BR(KLgponn)
L. Littenberg
E731
E799
KTeV
Phys. Rev. D61 (2000)
po  gg
SM Prediction
Year
Phys. Lett. B447(1999)

5. KL Decay Modes Decay Mode Branching Ratio Additional Particles popopo
p+p-po
p+m-n
p+e-n gg
ggg
pogg
pop+e-n
p+e-ng
p+m-ng
p+p-g
popog m+m-g
e+e-g
e+eｰgg
21.13 %
12.55 %
27.18 %
38.78 %
5.86・10-4
<2.4 ・10-7
1.68・10-6
5.18・10-5
3.62・10-3
5.7 ・10-4
4.61・10-5
<5.6 ・10-6
3.25・10-7
10.0 ・10-7
　 6.9 ・10-7 4g
2Ch 1g 2g 3g
　　 2Ch
Decay Mode
Branching Ratio
Additional Particles
poge+e-
p+p-
popo
m+m-
e+e-
p+p-e+e-
m+m-e+e-
e+e-e+e-
pom+m-
poe+e-
ponn
e+m-
e+e-m+m-
pom+e-
<7.1 ・10-7
2.06・10-3
9.27・10-4
7.15・10-9
9 ・10-12
3.5 ・10-7
2.9 ・10-9
4.1 ・10-8
<5.1 ・10-9
<4.3 ・10-9
<5.9 ・10-7
<4.7 ・10-12
<6.1 ・10-9
<6.2 ・10-9
1g 2Ch
2Ch 2g
4Ch

6. Detector Inefficiency
Inefficiency of g detection Inefficiency for charged particles
NIM A359 p478 (1995)
B.G. from KLgp-e+n Decay
Separating charged veto

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

8. KEK-PS E391a First dedicated experiment
Pilot experiment for next step (JHF)
Figure out sources of background
Developing method of rejection/estimation
Realizing detector setup in high vacuum system
Compact detector system
High acceptance
Pencil beam
Double decay chamber
Highly evacuated decay region
High PT selection

9. How far we have to go ? BR(KLg po nn) New Physics (?) Ke3, Kp3, Km3
KTeV
d Current Exp. Limit
hep-ph/
hep-ph/
hep-ph/
Limit from K+ g p+nn (PRL 84, 3768 (2000))
E391a
New Physics (?)
S. M. Prediction
JHF KOPIO(BNL)

10. E391a Detector Setup KL po n n gg Nothing
pure CsI calorimeter p veto system

11. Pencil Beam

12. Beam Profile

13. Layout of Beam survey H. Watanabe (2002) : Revised B.G. estimation
Thermal Neutron Detectors
(LiI, Li glass)
Hodoscopes
(15x15)
Profile detectors
KL monitoring using regeneration
Cerberus
BGO
KL monitor
Liquid Scin.
CsI
Copper
Lead glass
n/g detector
(SLSD)
Moving Rail
H. Watanabe (2002)
: Revised B.G. estimation

14. Schedule 2001 2002 2003 2004 CsI Front barrel Construction Beam Test
Main barrel
Construction
Vacuum
&
Cosmic Test
CsI
Assembling
Assembling
Detector setup
Beam survey
Engineering Run
Data Taking
Data Taking
Cosmic Run
Jan Apr Jul Oct.
Jan Apr Jul Oct.
Jan Apr Jul Oct.
Jan Apr Jul Oct.

15. Search a Measurement High flux of KL Large acceptance
Suppression of the Background
Standard model event
B.G. linear to beam intensity
 Same S/N ratio (~3)
New physics
Newly designed detectors system
Physical motivation
Following talk

16. JHF Large Number of KL Decay Three orders larger KL flux
Beam will be given from 2007
Two stages of construction
Limited beam lines
Many experimental programs
KL p0nn Measurement
Experiment at the first stage of JHF
Flexible approach

17. E391a at JHF Experience at KEK-PS Same veto system
Low cost, earlier starting
New calorimeter
resolution, clustering, efficiency
Fast DAQ
High counting rates
Optimization of beam line
KL/n/g ratio, L production
T.Inagaki　CP Violation in K Dec. (1998)

18. In future ・・・
BR(KLgponn)
E391a
SM Expectation
KOPIO
JHF
Year

19. Summary Golden channel to access CP violation (KL  p0nn) KEK-PS E391a
Pilot experiment for JHF
The first high sensitivity experiment
Plan for data taking on 2003
JHF
Real measurement of branching ratio
Most clean measurement of CPV parameter
Unitary triangle in K-system
Potential to access the New Physics
LOI within 2002 !