OJ - PARC E14 K TO Experiment
0for K L # " !!
Kyoto University
H. Nanjo
for KOTO collaboration

1Kaon09

J-PARC E14, KOTO

• KOTO = K0 at Tokai.

– The “koto” is a traditional Japanesemusical instrument (Japanese harp)– Collaboration• Japan-USA-Russia-Taiwan-Korea• 5 countries and 16 institutes, ~65 members.
• Based on KEK-PS E391a collaboration.

We aim to discover KL →π0ννwith the similar method
used in theE391a.

The diagram and J-PARC logo

2KEKKyoto
NDA
Osaka
SagaYamagata
Arizona StateChicago
Michigan
JINR
National TaiwanCheju
Chonbuk
Kyungpook
Pusan NationalSeoul
Kaon09Motivation

constraint from K L # " 0!!
(10% accuracy in Br)• Flavor Physics– Direct CP violation.
– Br(KL→π0νν) ∝ η2!

!

K+• η:Complex phase in CKM (Height of unitary triangle)• Beyond the SM– Rare FCNC process (highly suppressed in SM).
• Br(KL→π0νν)=(2.8 ± 0.4) × 10-11– Very Sensitive to new physics(TeV-ScaleKLPhysics).

!0• Small theoretical uncertainty– Short distance physics (>99% due to t quark)
Kaon093– ∼2% uncertainty in (Br →η)  Golden mode.

Room for New Physics

Br < 6.7 " 10 !8 (90%CL)– KEK-PS E391 Run2

– Run3 analysis  KOTO

– Grossman-Nir boundBr < 1.46 " 10 !9 (90%CL)– model independent (can be violated if LFV)
+1.15
!10– indirect limit from K+ →π+νν BNL E797/E949 Br = 1.73 !1.05 " 10MSSM
Little Higgs
with T-parity

Chance to reach TeV-scale New Physics with Kaon
4Kaon09

Concept of Experiment• KL beam(proton  target)– neutral beam line
» Long beam line  Kill particles with shorter lifetime» Charged particle sweeping magnet.
» Pb photon absorber  reduce beam photons» Collimator  shaping KL Pencil Beam(source of beam halo)– Core : KL, photon, neutron– Halo : neutron scattering on the surface of collimator
primary proton• Detector– π0 (→γγ) and nothing• Photon calorimeter and hermetic vetos.
• Pencil Beam Method. (smallbeam hole and KL rec.)Kaon095

Strategy from E391a to KOTO
• Requirement : 3 order improvement– (1)High intensity beam
– (2)New beam line (suppress halo neutrons)– (3)Detector upgrade (suppress background)MR
perimeter~1.6km
30 GeV for slow ext.
2×1014 ppp 0.3MW
0.7s spill/3.3s repe.

Exp Hall

Detector at
16 deg line

20m neutral beamline

proton
6T1 Ni Target
Kaon09(1) High Intensity Beam

7Kaon09

(1)High intensity beam
• Flux x RunTime x Acceptance = 3000 x E391
 2.8 SM events (3 order higher sensitivity than E391a)
KOTO

E391a (Run2)

Proton energy

30 GeV

12 GeV

Proton intensity

2e14

2.5e12

Spill/cycle

0.7/3.3sec

2/4secExtractionAngle

16 deg4 deg

Solid Angle

9µStr12.6µStr

KL yield/spill

7.8e6

3.3e5x30 /sec

Run Time

3 Snowmass years=12 months.

1 monthx10

Decay Prob.

4%2%x2

3.6%*

0.67%

x5

Acceptance*without Back splash loss

8KOTO

E391aKaon09

(2) New Beamline

9Kaon09

(2)New Beamline

21 m beamline
Finish the construction in this September including Shields
10Kaon09

New Beamline Concept– 16 deg extraction• X-Y asymmetric target image

T1 target

proton– Square detector beam hole

16 degKL : wider in X• Fit beam shape to the detector hole shape– rectangular beam hole to increase KL flux

– Pencil Beam  ~9µ str• beam size v.s. background– higher inefficiency for beam holeveto detector.

– Halo neutrons suppression• Collimator design Suppress scattering on the wall

– Control neutron hit rate for detectors near beam .
•  Accidental Loss  Collimator design
11Kaon09

Design Value
KOTOE391a

Halo neutron/spill(P>0.78GeV/c)

1.1x104

1.1x105

KL/spill

7.8x106

3.3x105

Halo neutron/KL

1.4x10-3

3.3x10-1

1/240– halo-n/KL : 1/240 of E391a

12Kaon09

(3)Detector Upgrade

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Kaon09

KOTO Detector
NCC• π0 and nothing– Calorimeter– Veto

Kaon09

Backgrounds at E391a• Understand Mechanism of BGs

E391 Run2• E391a and further study• Detector upgrade against them

KOTO box• E391a Run2 BG– Halo-neutron backgrounds

E391 box• CC02: 0.16±0.05 + (1.9±0.2)• CV-π0:0.08±0.04• CV-η0:0.06±0.02
Vertex shift due to energy leak

– Kaon backgrounds• Kπ2: 0.11±0.09

Vertex shift due to mass difference

Vertex shift due to energy contamination
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2 E1 E 2 (1 # cos " ) = m! 0

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Kaon09

E14 Background estimation• CsI shower including photonuclear effect is fully
simulated.
• Inefficiency functions are used for other vetoes.

Factor 2-3 uncertainty on KL yield we will measure in this fiscal year.
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Kaon09

CV Background• Two layer layout

Vertex shift due toenergy contamination– Far from signal region– Remove inner part50cm

• η reduction

25cm

Rear

Front
6mm

– Far from beam (Front)– Make thinner

3mmouter• 1/10 reduction for CV-π0Inner– more for η• halo-n/KL: 1/240• Further reduction using
CsI cluster shape.
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CsI
7x7x30cm

CsI
2.5x2.5x50cm
Kaon09

CV prototype• EJ212 with 1mm φ Y11• 1.3mm☐MPPC for high Q.E.
• 8 MPPCs are ganged

1.3x1.3mm– read as 1 channel.

• Light Yield : 5 p.e. /100keV
dark curent noize
Threshold at 100keV isfor 8 ganged MPPCs at 0 ℃ necessary to vetocharged 3π mode
4.5 p.e. threshold
Acceptance loss
due to dark current noise isnegligible for 0 ℃ operation.

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beam hole

WLS
Fiber
Kaon09CC02 background• halo neutron/KL reduction : 1/240 Vertex shift due toenergy leak• 50cm CsI  reduce shower leakage : 1/10
• Move upstream (30cm) :1/10halo neutron hit x10• NCC: CsI full active. :1/10• long interaction length to suppress n interaction.
• short radiation length to veto π0γγ• Veto with extra particles in π0 production.
– Segmentation for halo-n monitor with n/γ separation.

WLS fiber readout
19Kaon09

NCC prototype test
• 2mm φ PMP fiber x 20– UV absorption– blue emission• 3 parts of pure CsI WLS fiber– each CsI read by 2 fibers separately.

• 8 p.e. /MeV for 14 fibers.

68mm
20

150+200+100mm Kaon09

• Granular CsI

Kπ2– Fusion• Longer CsI– 30cm50cm– punch through• MB (Barrel Photon Veto)– Thicker

E391a• 14X0  18.5X0

KOTO• Even and Fusion BG– 2 γ missed in MB
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Kaon09Other Activities

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Kaon09CsI Calorimeter• CsI

All CsI crystals and phototubes were shippedto Osaka (+Chicago) for light yield tests.
Outer edge region Sandwich detector
Pb 2mm/Scinti 5mm

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Kaon09CsI Calorimeter Readout
Differential outputs
Shielded Twisted Pair Cable

Low voltage supply

Custom 125MHz FADC
(with Gaussian Filter)
FPGAPMT

Amp. + CW baseused inside Vacuum low power consumption(150mW)

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Kaon09Beam Hall Photon Veto
• Lead gamma converter + Aerogel Cerenkov radiatorN insensitive to neutrons.
C• We already tested a prototype.

C– 2-way light readout for the next production.

n: 0.4 GHz
γ: 0.6 GHz

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Kaon09Schedule10-8• 2009– Beamline construction– Beam survey• 2010
10-11– CsI calorimeter1018construction– Engineering Run with CsI
calorimeter

1021• 2011– Physics Run Start.
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Kaon09

Summary• KOTO experiment to discover KL →π0νν.
– Understand backgrounds in E391a  Strategy tothe discovery.

• Neutral beamline design was fixed and theconstruction is in progress, will be finished inthis September. Beam survey in this year.
• Detector upgrade is being designed andprototype is made, tested toward Engineering
run in 2010 and Physics run in 2011.
• We will start to investigate TeV-scale physics
just after the start.
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Kaon0928

Kaon09Beam Survey Preparation• KL yield measurement– charged Kπ329

Kaon09Preparation• EM(Pb/Scinti) and Hadron(Fe/Scinti)
sampling calorimeter30

Kaon09Collimator Design•

1 Collimate core beam  KL/neutron/gamma– Pencil beam : ~9uStr•

2 Suppress halo-n from Pb, Control core-like neutron (single scattering)• Scattering at Pb absorber  2nd Collimator– Hide the surface of 2nd Collimator from Pb absorber to reduce halo-n•3 Suppress halo-n from hot spot, Control halo neutron (multiple scattering)– Hide the rear part of 2nd Collimator from hottest place to reduce halo-n.
 core-like increased, keeping detector hit rate low enough.
detector
Ni target

beam holePb absorber
1st Collimator

2nd Collimator
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Kaon09

Ke+3KL

π− CEXe+annihilation
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Kaon09