The new KL experiment (KOTO) at J-PARC

Hiroaki Watanabefor the J-PARC E14 KOTO collaboration

KEK, IPNS

J-PARC E14 KOTO Collaboration

• Arizona State Univ.• Cheju National Univ.• Chonbuk National Univ.• Univ. of Chicago• Joint Institute for Nuclear Research(JINR)• KEK• Kyoto Univ.• Kyungpook National Univ.

16 Institutes from 5 countries. 62 collaborators.

KOTO: K0 at TOkai. • Univ. of Michigan, Ann Arbor

• National Defense Academy• Osaka Univ.• Pusan National Univ.• Saga Univ.• Univ. of Seoul.• National Taiwan Univ.• Yamagata Univ.

Measurement of Br(KL )

)Im(2)( **0

tdts

tdtststdL

VVVVVVKA

110 10)4.05.2()( SMLKBr

The clean process :

1 ～ 2 % theoretical uncertainty

Sensitive to New Physics.

Amplitude of CP-violation in Quark Sector.

0LK

0

s t

t d

d

0ZVtd

F. Mescia and C. Smith updated in June, 2010.

Strategy Step by Step approach.

KEK-E391a (previous experiment) Establishment of experimental method.

J-PARC Step-1 (E14 KOTO)

First observation. Search for enhancement

by New Physics.

J-PARC Step-2 > 100 events

E391a-final

Experimental Method

KL

Proton

2 + Nothing

KL

1 . Hermitic veto with high detection efficiency: To count number of photons. - KLis most serious background by missing 2 .

2. Pencil Beam : to obtain kinematical constraints. KL decay on Z-axis. - reconstruction of decay vertex(Zvtx) and transverse momentum(PT) of

Surrounding with veto counters

KL collimators

Calorimeter(CsI crystals)

• Number of KL decay

• Signal Acceptance

• Single event sensitivity

Br(KL ) < 2.6X10-8

PRD 74,051105(R) (2006)PRL 100,201802 (2008)PRD 81,072004 (2010)

Previous experiment: Sensitivity in KEK-E391a

Previous experiment: Backgrounds in KEK-E391a

*More detail can be seen in Poster session.

Halo neutron + detector material0 + X ( or + X)

J-PARC KOTO : Sensitivity and background

• Intense proton beam at J-PARC:– New accelerator .– Longer physics run.

• New KL beamline: 16o extraction.

– Softer KL beam. Decay prob.

– n/KL ratio: 456.5.– Softer neutron beam: x0.13 due to reduction of production probability.– Optimized optics to suppress halo neutrons: Halo-n/KL =0.07%, 1/240 of E391a.

• Upgraded detector and electronics: – Longer and finer segmented CsI crystals ( loaned from KTeV at Fermilab).– Improved veto counters.– New pipeline-readout flash ADC for high rate. – x3.6 acceptance is expected than that of E391a.– 2x10-6 reduction of halo-neutron background by detector upgrades.

• 3 events are expected. – 2.5 background events are expected. (backgrounds are dominated. Halo-neutron event is negligible.)

J-PARC KOTO

KEK-E391a improvement

KL yield/spill 8.1x106 3.3x105 x30/sec

Run time 12 months 2 months x6

Decay prob. 4% 2% x2

Acceptance 3.6% 1% x3.6

Sensitivity 0.8x10-11 1.1x10-8 x1300

30 GeV Synchrotron

3 GeV Synchrotron

LinacJ-PARC(Japan Proton Accelerator Research Complex)

2x10 14 protons/spill, 1spill=3.3sec.

(design value).

Item J-PARC E14 KOTO KEK-E391a

• Primary proton energy 30 GeV 12 GeV• Proton intensity(/spill) 2x1014 2.5x1012

• Spill-length/repetition 0.7s / 3.3s 2s / 4s• Production target Common “T1” Pt rod• Extraction angle 16 deg. 4 deg.• KL yield(/spill) 8.1x106 3.3x105

• Average PKL 2.1 GeV/c 2.6 GeV/c• n/KL ratio 6.5 45

Parameters of beam

Momentum dist. of KL. Momentum dist. of Neutron

p

Layout of the KL beamline at J-PARC

30GeV Proton

T1 target

Photon absorber1st collimator(4m-long)

Sweeping magnet

Beam plug

2nd collimator(4.5m+0.5m-long) KOTO detector

Key: Halo neutron produced by multiple scattering at inner surfaces of collimators.1. Primary collimation to form beam core shape and size.2. Trimming collimation to suppress scattered neutron at upstream hot regions.

Collimator optimization.

　･ Halo neutron/KL : 0.07% ( E14-request : <0.13% ) (1/240 reduction than E391a)

Detector Upgrade.KEK-E391a, 30cm-long (16X0)

J-PARC KOTO(loaned from KTeV),50cm-long 27X0

Lead/plastic-scintillator segmented CsI’s.(1/20 reduction of halo-neutron B.G.)

γ

γ

Reconstruction-vertex

4x10-5 reduction of halo-n B.G.

• Assuming 12 months of physics run=1.8x1021 protons on target – 3 events are expected – 2.5 background events are expected.– S/B = 1.2

B.G. source No. of B.G events. • Other KL decay KL0 1.8 KL0 0.4 KL-e+ 0.005 KL negligible KL0 negligible

• Neutron Interaction With Residual gas 0.04 At the CC02 0.01 At the C.V. negligible Accidental coin. 0.10

MC: KL0

Preparation status

• Beamline construction in 2009.

• CsI-calorimeter construction in 2010.

• Completion of whole detector in 2011.

• First Physics Run in 2012. – Reaching GN-limit, 1.5x10-9.

Beam plug

Dipole magnet

1st collimator（ 4m-long ）

2nd collimator(4.5+0.5m)

Photo in July, 2009

beam

18

Upstream

Exit of KL beamline

Downstream

KL1: KL+-0 measurement using hodoscopes and mini-calorimeter

KL2: KL+- by spectrometer

Beam profile monitor

Core Neutron/gamma meas.

Beam survey: Nov. 2009 ～ Feb. 2010.6×1011 ～ 2×1012 protons/spill (1spill=6sec)

Measurement of KL Yield by detecting KL0

1905 events were observed.1.83x107 KL’s/2x1014 p.o.t.(*preliminary number)

It corresponds to • Proposal-yield x 2.3 (*MR DCCT normalization)

*More detail can be seen in Poster session.

Reconstructed Mass. Reconstructed KL Momentum

No data for 16o extraction at 30GeV.Big differences betw. M.C. simulations.

MC package #KL/2E+14potGEANT3 1.5x107

GEANT4(QGSP) 0.88x107

GENAT4(QBBC) 1.0x107

FLUKA 3.2x107

Beam profile

Overall beam shape is well reproduced by M.C. simulation.

PWO, CsI crystals

Calorimeter construction Vacuum chamber

PMT holder installation

Stacking of CsI crystals

Summary and prospect• J-PARC KOTO aims at First Observation( ～ 3 events) of KL0 using:

– High intensity proton beam at J-PARC,– New KL beamline,– Upgraded detector + new fast electronics.

• Beamline construction and survey was completed in 2009.– x2.3 KL yield compared to that of the proposal has been observed.– Beam shape is well reproduced by M.C. simulation.

• Stacking of CsI calorimeter has been started.

• Engineering run with CsI’s and new readout system will be started in Oct.,2010.

• In 2011, whole detector system will be completed.• In 2012, first physics run will be started. reaching the Grossman-Nir limit, 1.5x10-9.

backup

J-PARC at Tokai mura

July, 2009

Pacific Ocean

T1 target

K1.8

K1.8BR

K1.1

KL

K1.1BR 30GeV Primary Beam

Productiontarget (T1)

Plan View: Hadron Experimental Hall

Baryons in Nuclei

Mesons in Nuclei

Beam Dump（ Movable on the Rail)

Rare Decay

Mesons mass/ Time reversal

High Momentum

Beam Line

Beam

○ 54mm-thick pure-Nickel.　　 It divided in to 5 disks 21.7, 11.2, 8.3, 6.9, 5.9○ Beam Energy: up to 50 GeV.○ Beam Size : X,Y : 1.3mm○ Target is cooled by water in 1 atm.

T1 common target

July 11

August 7

beam

beam

beam

Beam test of CsI’s and electronics• 144 Channels were tested by positron beam

– Performance test for complete set of read-out– CW-base, 125MHz FADC, Trigger board– Figure out problems, confirm no problem for stacking

Calorimeter preparation

Positron Energy(MeV)

Ener

gy R

esol

ution

(%,

/E)

PT3

Proposed Detector Upgrade( cont’d)Acceptance loss by BHPV due to accidental hit: 30~40 %(E391a 2E+12ppp)

2 % (E14, 2E+14ppp)

Lead / Aerogel Cerenkov radiator99.9%

CsI Read-out