Measurement of KL decay

G.Y.LimIPNS,KEK

Why KL→? Flavor Changing Neutral Current

Br(KL o ) = 6 1 ・ Im(VtdVts)2X

2(xt)

= 1.94 ・ 10-102A4X2

Strong Interaction : Factorized by Ke3 Decay

Very Small Theoretical Uncertainty

Negligible Charm contribution

In JHF era

Unitarity Triangle vertices Beyond Standard Models

K+

KL

ACP(BJ/KS)MBd/MBs

G. Buchalla hep-ph/0110313 L.Littenberg HEPAP(2001)

E391a

Search for the decay KL

e+e-

Phys. Lett. B447(1999)

Phys. Rev. D61 (2000)

SM Prediction

L. Littenberg

E731E799

KTeV

BR

(KL

o )

Year

Decay Mode

Branching Ratio

Additional Particles

oo

+o

e

+ee

e+e

e+e ｰ

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

4 2Ch 2Ch 2Ch

1 2 2Ch 2Ch 2Ch 2Ch 3 2Ch 2Ch 2Ch

Decay Mode

Branching Ratio

Additional Particles

e+e

ee

ee

ee

eeee

ee

e

eee

<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

1 2Ch 2Ch 2 2Ch 2Ch 4Ch 4Ch 4Ch 2Ch 2Ch

2Ch 4Ch 2Ch

KL Decay Modes

Inefficiency of detection Inefficiency for charged particles

Detector Inefficiency

NIM A359 p478 (1995)

B.G. from KL-e+ Decay

Separating charged veto

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

http://psux1.kek.jp/~e391/index.html

E391a Collaboration

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

How far we have to go ?

Ke3, K3, K3

KTeV

E391a

JHF KOPIO(BNL)

S. M. Prediction

BR

(KL

o

)

Current Exp. Limit

New Physics (?)

Limit from K+ +PRL 84, 3768 (2000))

hep-ph/9908399hep-ph/9804412hep-ph/9808487

E391a Detector Setup

KL Nothing

pure CsI calorimeter 4 veto

system

Pencil Beam

Beam Profile

Layout of Beam survey

Moving Rail

Hodoscopes (15x15)

Profile detectors

Cerberus

Thermal Neutron Detectors (LiI, Li glass)

CsI

n/ detector (SLSD)

Lead glass

KL monitor

Liquid Scin.

BGO

Copper

KL monitoring using regeneration

H. Watanabe (2002)

: Revised B.G. estimation

Schedule Schedule

2001 2002 2003 2004

Data TakingAssembling Detector setup

Vacuum &

Cosmic TestAssembling

Front barrel Construction

Main barrelConstruction

Cosmic Run

Beam survey Engineering Run

Beam Test

Data Taking

Jan. Apr. Jul. Oct. Jan. Apr. Jul. Oct. Jan. Apr. Jul. Oct. Jan. Apr. Jul. Oct.

CsI

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

Search Measurement

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 Measurement Experiment at the first stage of

JHF Flexible approach

JHF

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/ ratio, production

T.Inagaki CP Violation in K Dec. (1998)

In future ・・・

E391aSM Expectation

KOPIO

JHF

Year

BR

(KL

o )

Summary

Golden channel to access CP violation (KL 0) 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 !