KOTO実験によるK中間子稀崩壊探索南條 創(京都大学)

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Contents
Motivation● KOTO Experiment● Prospect●2

Motivation

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New Physicsはあるのか？

4●2008 : Kobayashi and Maskawa– CP-violation was established.
– The size is not enough to explain matter dominant universe.
– New CP-violating particle is expected in higher energy scale.

●2013 : Englert and Higgs– Higgs was discovered but it is far from closing the book.
– New physics in high energy scale is expected to stabilize Higgs mass.
– SUSY, little Higgs, Compositeness, Extra Dimension, …?
– Dark matter?
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●

New Physicsは存在する。
– 物質優勢宇宙– Dark Matter– ...

●どうやって探す？

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New Physics Search●High Energy Frontier ↔ High Intensity Frontier– High energy frontier → direct production of heavy particle– High intensity frontier → indirect access, high energy reach

一瞬の高エネルギースケール→稀なプロセス

標準理論の抑制● GIM, CKM,Helicity...suppression● 精密な理論予測●●

Multi-process approach 多方面からフレーバ構造を明らかに●●

Correlation is important.

CP-violation is another guide.
explanation of matter dominant universe7

Why Kaon?
●Blanke '13“Generally most powerful”– GIM suppression of u and c quarks– Hierarchical structure of CKM for t quark●Most suppressed in s → d transition (λ5)– b → d (λ3) , b → s (λ2)

uctds

例えBs/d → μμがSM-likeであっても、s → dはNPでエンハンス可能

b8

Bona '07
Ishidori '13

Energy Reach

Flavor structure

MFV

Generic

Tree/Strong couple

5TeV

24000 TeV

Loop αS

0.5 TeV

2400 TeV

Loop αW

0.2 TeV

800 TeV

Tree/Strong couple ~1
Loop αS~0.1
Loop αW~0.03(Bona '07)

Genericの場合、K sectorが最強 → 104 TeVまでのリーチ
なぜまだ見えない？ ↔ Energy scale, Flavor構造
Minimal Flavor Violation likeな場合、Bと強い相関
9(NPでもCKMの構造を保持,新しいCPV phaseもない)NP > 1 TeV? (ATLAS,CMS)● Non-MFV like ? (LHCb,CMS)●Buras'13

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●Rare decay–●Strong suppression from CKM

Buras '15

Small theoretical uncertainty ~2%–High energy scale–

Hadron matrix element from tree process Ke3/Kmu3

Sensitive to new physics beyond the SM●

CP-violating process●

Related to charged mode
–Grossman-Nir bound :●Model-independent inequality w/ iso-spin rotation

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Status10-8

Direct limit
2.6x10-8 (KEK E391a)

10-9

Indirect limit
1.5x10-9 (Grossman-Nir)

10-10

New Physics?

10-11

SM sensitivity
2.4x10-1112SM extension w/ 4th generation→ ruled out
Direct search
EW precision test
Higgs mass

Otto '1213

from
ΔS=2とΔS=1のNPによる変化→ 同じnew phaseが支配Z'/Z with Left / Right-handed coupling
Littlest Higgs with T-parity

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Input from ε'/εDirect CPV from KL → ππ
Progress from lattice calculation

Buras '15
SM expectation(Theory)

Left and Right-handed coupling
still can enhance Br(KL)MFV
Left or Right-handed coupling15

EW penguin contribute to e'/e in negative interference.
Negative correlation btw Br(KL)Buras '15

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Buras '15

Left- and right-handed coupling model can enhance Br(KL)17

Buras '15

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Littlest Higgs with T-ParityBlanke '15

Symmetry breaking scale

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SUSY at 10-50 TeV

Tanimoto,
Yamamoto '15

10 TeV SUSY → still large enhancement on Br(KL)●Less correlation btw Br(KL) and ε●– 50TeV SUSY still have enhancement factor on Br(KL)20Weekly-coupled light Z'with Lμ – Lτ coupling●Fuyuto '14

Explain g-2 with Mz'<400MeV– also relate to B → Kμμfrom E949 experiment

KOTO already access here.

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KOTO Experiment22

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KOTO : K at TOkai●Extraction

J-PARC Accelerator– High power ↔ Statistics of rare process– Slow extraction ↔ Event pile-up due to high rate●

J-PARC 33kW (June 2015) ~ World-highest class

3GeV30GeV

400MeV23

Fixed Target Experiment●High intensity proton beam+ Primary target– High intensity secondary products●Beam line
– Transport particles of interest●Reduce unwanted particles– Long life to transport.

Gold 15mm x 6mm x 66mm
30 GeV proton

24Particles mass and life time
BottomStrangeCollider(τ、D,B,t)Tools for fixed target experimentwith high intensity proton driver
Lower mass
Longer life timeKaon

has bee a special tool
for fixed target experiment

Pion
Neutrino source
Muon source

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Kaon
Low mass (0.5 GeV)
● Long life time (15m)● StrangenessGood for fixed target→ Flavor Changing Neutral Current●●s → d transition– Flavor changing neutral current (GIM)– Strong CKM suppression●KL → π0νν (Br 3x10-11 in SM)– Direct CP-violation

26Beam line
金標的 + proton● KL beam line
●電磁石 (charged)● 20m長尺 (short-lived)● コリメータ (beam halo)●→ 細くシャープな中性ビーム(KL, γ, neutron)“Pencil Beam”
33kW
6sec cycle

4x10 proton13

立体角 7.8μsr~40%lost by decay~107 KL

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2nd collimator(4.5+0.5m)

Beam plug

1st collimator（4m-long）
Dipole magnet

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Signal Reconstruction
2γ+nothing → Calorimeter +● Beam constraint→ “pencil beam”●Veto detectors

6.1m

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Detector~2m

Veto : γ/charged
10-4 – 10-6 reduction

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History

100hours

Detectorupgrade31

1st physics run in 2013

CKM2014

Sensitivity : 1.29x10-8 (Preliminary)~ E391a sensitivity with only 100-hour run

1 event
in the signal box
87
Number of observed data
→ Well understood.

87

10.2±0.1

97.2±0.5

32Main background source in E391a
Halo neutron → π0 at
Upstream detector
Downstream detector→ Largely reduced.
E391a Final (5month)
S.E.S : 1.11x10-8

KOTO 1st Physics run(4days)
S.E.S : 1.29x10-8878710.2±0.1

97.2±0.5
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Background source in KOTO8787

10.2±0.1

97.2±0.5

CC05

CC06

Beam pipe1m34

Run in April-June 2015
●Physics run● 5.3 times higher POT ↔
run in May 2013

●Calibration and special runs
Calibration,Special runs

Physics run in 2015
33kW
29kW
26kW

Physics
24kW

26kW

X5.3

Integrated POT for May 201335

0Check with 3π sample• Calorimeter and KL properties
consistent with the run in May 2013.
• More detailed calibration is on-going• Study to suppress background

Area normalized

Black :April-May 2015
Red :May 2013

Area normalized36

To suppress halo neutron●Upstream beam window
Kapton 125um → 12.5um– Reduce neutron scattering–●

Re-alined collimator– Reduce neutron scatteringon the collimator inner surface

Hadron interaction events37Collimator alignment withnew beam profle monitor

Lead(1.5mm)

MirrorPhosphor
plate

Re-alined collimators38

To understand hadroninteraction events
Scattered at the target
Core neutron
10 mm thick Al

Contribution by
Chonbuk Univ.
* Removed in physics run
Took Al-target data 70 hours> 15 times higher statics
than May 2013

Hadron interaction

Gammas from π0

Reconstructed PT(MeV/c)
Reconstructed Z vertex(mm)

39Developing BG reduction with cluster shapeTo suppress low P T events
CC05

CC06

Beam pipe
Plastic scintillator
WLS fiber
1mPMT●

Beam pipe (5mm t)
SUS → Aluminum●

Installed Beam Pipe Charged Veto
Plastic scintillator 5-mm thick– Wavelength shifting fber readout–~1/60 reduction expected40

To suppress KL → 2π0

Added modules
X0: 4 → 6.2
Photon punch-through inefficiency→ 1/5

In-beam photon veto
Lead and Aerogel
Cherenkov detector

Lead and Acrylic
Cherenkov detector

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Prospect42

0To suppress KL → 2π more
• Install inner barrel detector in winter 2015
• Add 5 X0 to 13.5 X0 of current Main Barrel– Suppress punch-through ineffciency by 1/50.

Gluing fber to scintillator was mostly fnished.
Module assembly will start soon.
Will install it in this winter+ Maintenance for existing broken channels in vacuum
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Plan
• NA62 will take 100 events toward 2017 for– Push Grossman-Nir limit down.
• We will overcome our background and improve our sensitivity

2015 April-June2015 Fall2016
201744

Long term plan

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Summary
New physics scenario

KOTO– MFV or non-MFV?

– 1st Physics run in 2013

●MFV likeBr(KL→π0νν) ↔ ε'/ε > SM? will suppress
Br(KL) enhancement– Strong correlation pattern from εK–●

Non-MFV with only left or right-handedcoupling– Similar to MFV●

Non-MFV with left and right-handed coupling– Z' model , generic SUSY, .. → will still enhanceBr(KL) largely– NP in 5 TeV still enhance Br(KL) largely– SM extension with 4 generation→ ruled out– Littlest Higgs with T-parity→ under pressure from B→μμ
– KOTO already have discovery potential
for light Z' with ~π0 mass

Sensitivity ~ current limit with only 100
hours data
● New background mechanism → neutron●– Restarted in 2015

already took 5.3 times larger statistics● Data to study neutron background● Calibration and study to suppress neutronbackground●– Prospects

Will overcome neutron background● Will search O(10-11) area for Br(KL) ~2018● Continue to KOTO Step2 in enlarged
Hadron Experimental Facility●46