Status of the E391a experiment
その１Hiroaki Watanabe
University of Chicago

Outlinez Introduction
zPhysics Motivationz KEK-E391a
zMethodzApparatus
zSchedule
zPreparation
zDetector Constructionz SummaryooKLÆπνν
Theoretical BackgroundoLo〜Theoretical Background 〜K ÆπννBr( KL0 → π 0νν ) ≈ 1.8 ×10−10 ⋅η 2 ≈ 3 ×10−11¾Flavor Changing Neutral Current¾Direct CP violating process ( Δs = 1 )¾Theoretical uncertainty : Very Small! ( ~ few % error)¾The hadron matrix element can be factorized
as the well-know KÆπeνdecay!

¾One of best tool to determine
CP-violation parameter, η¾Clue for the new physics

oLoK ÆπννKL0 ≡ εK K1+K2 ≈ K2 = K0 − K 0⇒ A(KL0 →π 0νν ) ≈ A(K0 →π 0νν ) − A(K 0 →π 0νν )∝ V - Vtd ∝ Im(Vtd ) = η*td

BSM effectFor example:

Unitarity Triangle verticesη

If SUSY ( MSSM ) effect exists…

ε

hep-ph/9908499¾Contribution ＜~10%¾Correlation¾ε Æ enhanced∆MBd/∆MBs
K+ Æ π+ννKL Æ π0νν¾ Br(KÆπνν)Æ suppressed¾ΔＭＢｓ、Ａ（ＢÆJ/ψKs)

ACP(BÆJ/ΨKS)
G. Buchalla hep-ph/0110313、

Æ unchangedρ

These correlations strongly depend on the Model!
Combination of K decays and B decays might give clue for new physics

ooKLÆπνν
Experimentally Challenges

Br(KLÆπ0νν）〜 3 x 10-10Br(KLÆγγ) = 5.86 x 10-5Br(KLÆπ0π0） = 9.27 x 10-4γγγγ

γγ + nothing
γγ (PT=0)
Pencil Beam(KL) ÆEnergy, Position of γ?
Æ Decay Vertex, PTγＫＬγ

The largest background rejection power :Veto on extra γDetection efficiency ~99.99%

One more things…Beam-related backgrounds
00Single π is copiously produced by n+nÆn+n+πγγHalo nγnγnResidual gas¾ Clean beam
 Low(beam halo↓)-5vacuum pressure 10 Pa.

Important Issues• Detector– Highly Hermetic Æ 4π coverage with thick calorimeter.
– Better γ veto Æ 〜1 MeV threshold• Beam line

– Tightly-collimated KL beam
– Clean beam … low neutron halo! Æ 5 stage collimation• Low vacuum pressure operation
Æ whole detector in vacuum– Based on these points…

KEK-E391a Experiment〜First Dedicated Search〜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
Joint Institute for Nuclear Research (Dubna) Russia
Department of Physics, University of Chicago
Fermi National Accelerator Laboratory
Department of Physics, Pusan National University

2004/3/8

10 Institutes from 4 countries, over 50 collaborators.

KEK-E391a experiment
Target: Single Event Sensitivity

Br(KLÆπ0νν）〜 3 x 10-10
current upper limit : 5.7x10-7 by FNAL-KTeV
Standard Model prediction : Br 〜3x10-11

Pilot experiment for J-PARC era¾Verify our method¾Unexpected source of background¾Signatures of backgrounds
Experiment has been started from Feb. 2004 !

New K0 beam line for E391a

The Construction was finished on March, 2000

E391a Detector Layout

Upstream
section

KLMiddle Sectionπο ν νγγ

Downstream
sectionNothing

pure-CsI calorimeter

4π veto system

Upstream

Downstream

MiddleSchedule
Proposal was submitted in 1996.
Front barrelConstruction

Main barrel
Construction

Beam Test

VacuumCsI

Assembling

Assembling&Cosmic Test

Data Taking
Ｄｅｔｅｃｔｏｒ
Ｉｎｔｅｇｒａｔｉｏｎ

Engineering Run
Beamline upgrade
Jan.

Apr.

Jul.

2001

Beam survey
Oct.

Jan.

Apr.

Jul.

2002

Oct.

Jan.

Apr.

Jul.

2003

Oct.

Jan.

Apr.

Jul.

2004

Oct.

Upstream proton beam line

Target Station

First Collimators

Last Collimators

Beam profile
Counter Telescope

Very Clean !

Detector Construction
Experimental Area

Downstream Vacuum VesselAssembling of CsI calorimeter

Sep. 5,
2002
July,
2002
EndEndofofAugust,August,2002
2002
Crystal-Position CheckAugust, 2002
Sep 18, 2002

Assembling of Charged-particle Veto
Plastic Scintillator

Engineering Run (Nov - Dec, 2002)¾Purpose¾Overall check of detector system¾Endcap Part ( ~50% channels )CsI, Charged-Veto, CC03, BA
DAQ checkÆ working property¾Electric Noise¾Energy Calibration¾1. Cosmic-ray (+ Punch-through muons)¾2. π0 production by neutron interaction with metal.
¾Kaon measurement.
¾Kaon flux, momentum distribution…etc

Engineering Run
Energy Calibration
Step 1: Cosmic-ray & punch-through muonsÆ We can set the gainwith accuracy of ±5%
Æ This gain can be used as
inputs for next step.

Kaon RunoLo ooK Æπππ6-clusters events

σ~5MeVDetector Construction〜Barrel Part〜upstream

Detector Construction

Downstream

MiddleBarrel Fabrication

Ultraviolet lightFabrication of Front-Barrel Modules

The fabrication of the Front Barrel modules : ~Dec 17, 2002.
The fabrication of the Main Barrel modules : ~Sep 24, 2003.

Barrel-module Fabrication

The fabrication of the Front Barrel modules : ~Dec 17, 2002.
The fabrication of the Main Barrel modules : ~Sep 24, 2003.
2004/3/8

Cosmic-ray test of single barrel module

Average : ~14 photoelectrons/MeV-deposition at CenterFront Barrel Assembling

Sep. 5, 2003

Main Barrel Assembling

Dec 17, 2003

Detector Integration

Jan 22, 2004

Vacuum

Region 1 Region 2
10Volume (V, m3) 100
Surface (A, m2) 220
40

Vacuum

Schedule
Proposal was submitted in 1996.
Front barrel
Construction

Main barrel
Construction

Beam Test

VacuumCsIAssembling

Assembling&Cosmic Test

Data Taking
Ｄｅｔｅｃｔｏｒ
Ｉｎｔｅｇｒａｔｉｏｎ

Engineering Run
Beamline upgrade
Jan.

Apr.

Jul.

2001

Beam survey
Oct.

Jan.

Apr.

Jul.

2002

Oct.

Jan.

Apr.

Jul.

2003

Oct.

Jan.

Apr.

Jul.

2004

Oct.

Cosmic-ray test

Summary for Status Report その１
All detector constructions and its integration were completed !!!
All system including Detectors, DAQ and Vacuum
are properly working !!!
First beam was delivered on Feb. 17th, 2004
Æ Status Report そのⅡ presented by Sugaya-san, Osaka-U

Current Experimental Limito oSearch for the KLÆπνν decayπο Æ e+e- γBR(KLJπoνν)

10 −1

Littenberg

E731
E799

10−5KTeV
Phys. Rev. D61 (2000)πο Æ γγ10−10SM Expectation
10−1519902000Phys. Lett. B447(1999)

Engineering Run

Delay cables

electric noise

50 fC/ADC-ch

CP violation in the Standard Model+

L = − g 2 uiLγµ (VCKM)ijdjLWµ + h.c.
+CP(L) = − g 2 uiLγµ (VCKM)*ij djLWµ + h.c.
2λAλ3(ρ − iη)⎤⎛ d ⎞⎛ d′⎞ ⎛Vud Vus Vub ⎞⎛ d ⎞ ⎡ 1− λ 2⎟⎜ ⎟ ⎢⎜ ⎟ ⎜⎥⎜ ⎟22λ1− 2−λAλ⎜ s′ ⎟ = ⎜Vcd Vcs Vcb ⎟⎜ s ⎟ ≅ ⎢⎥⎜ s ⎟⎜ b′ ⎟ ⎜V V V ⎟⎜ b ⎟ ⎢ Aλ3(1− ρ − iη) − Aλ2⎥⎜⎝ b ⎟⎠1⎝ ⎠ ⎝ td ts tb ⎠⎝ ⎠ ⎣⎦η Standard Model

CP ViolationÆ ηVudVub

Vtd Vtb** ⇒VcdVcb*ρ