The new K L     experiment (KOTO) at J-PARC Hiroaki Watanabe for 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: K 0 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(K L    ) The clean process : 1 ～ 2 % theoretical uncertainty Sensitive to New Physics. Amplitude of CP-violation in Quark Sector. V td

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 KLKL    Proton 2  + Nothing K L    1. Hermitic veto with high detection efficiency: To count number of photons. - K L         is most serious background by missing 2 . 2. Pencil Beam : to obtain kinematical constraints.  K L decay on Z-axis. - reconstruction of decay vertex(Zvtx) and transverse momentum(P T ) of    Surrounding with veto counters K L collimators Calorimeter (CsI crystals) Calorimeter (CsI crystals)

Number of K L decay Signal Acceptance Single event sensitivity Br(K L    ) < 2.6X10 -8 PRD 74,051105(R) (2006) PRL 100, (2008) PRD 81, (2010) Previous experiment: Sensitivity in KEK-E391a

Previous experiment: Backgrounds in KEK-E391a *More detail can be seen in Poster session. Halo neutron + detector material   0 + X ( or   + X)

J-PARC KOTO : Sensitivity and background Intense proton beam at J-PARC: – New accelerator. – Longer physics run. New K L beamline: 16 o extraction. – Softer K L beam. Decay prob. – n/K L ratio: 45  6.5. – Softer neutron beam: x0.13 due to reduction of production probability. – Optimized optics to suppress halo neutrons: Halo-n/K L =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-E391aimprove ment KL yield/spill8.1x x10 5 x30/sec Run time12 months2 monthsx6 Decay prob.4%2%x2 Acceptance3.6%1%x3.6 Sensitivity0.8x x10 -8 x1300

30 GeV Synchrotron 3 GeV Synchrotron Linac J-PARC (Japan Proton Accelerator Research Complex) J-PARC (Japan Proton Accelerator Research Complex) 2x10 14 protons/spill, 1spill=3.3sec. (design value). 2x10 14 protons/spill, 1spill=3.3sec. (design value).

ItemJ-PARC E14 KOTO KEK-E391a Primary proton energy 30 GeV12 GeV Proton intensity(/spill) 2x x10 12 Spill-length/repetition0.7s / 3.3s2s / 4s Production targetCommon “T1” Pt rod Extraction angle16 deg. 4 deg. KL yield(/spill)8.1x x10 5 Average P KL 2.1 GeV/c2.6 GeV/c n/K L ratio Parameters of beam Momentum dist. of K L. Momentum dist. of Neutron p

Layout of the KL beamline at J-PARC 30GeV Proton T1 target Photon absorber 1 st collimator (4m-long) 1 st collimator (4m-long) Sweeping magnet Beam plug 2 nd collimator (4.5m+0.5m-long) 2 nd 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/K L : 0.07% ( E14-request : <0.13% ) (1/240 reduction than E391a)

Detector Upgrade. KEK-E391a, 30cm-long (16X 0 ) J-PARC KOTO(loaned from KTeV),50cm-long 27X 0 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 =1.8x10 21 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 K L     K L       K L   - e KL   negligible KL       0 negligible Neutron Interaction With Residual gas 0.04 At the CC At the C.V. negligible Accidental coin MC: K L   0

Preparation status Beamline construction in CsI-calorimeter construction in Completion of whole detector in First Physics Run in – Reaching GN-limit, 1.5x10 -9.

Beam plug Dipole magnet 1 st collimator （ 4m-long ） 2 nd collimator ( m) Photo in July, 2009 beam

18 Upstream Exit of KL beamline Downstream KL1: K L   +  -  0 measurement using hodoscopes and mini-calorimeter KL2: K L   +  - by spectrometer Beam profile monitor Core Neutron/gamma meas. Beam survey: Nov ～ Feb ×10 11 ～ 2×10 12 protons/spill (1spill=6sec) Beam survey: Nov ～ Feb ×10 11 ～ 2×10 12 protons/spill (1spill=6sec)

Measurement of K L Yield by detecting K L       events were observed.  1.83x10 7 K L ’s/2x10 14 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 K L Momentum No data for 16 o extraction at 30GeV. Big differences betw. M.C. simulations. MC package#KL/2E+14pot GEANT31.5x10 7 GEANT4(QGSP)0.88x10 7 GENAT4(QBBC)1.0x10 7 FLUKA3.2x10 7

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 K L   0 using: – High intensity proton beam at J-PARC, – New KL beamline, – Upgraded detector + new fast electronics. Beamline construction and survey was completed in – x2.3 K L 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.

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J-PARC at Tokai mura

July, 2009 Pacific Ocean

T1 target K1.8 K1.8BR K1.1 KL K1.1BR 30GeV Primary Beam Production target (T1) Plan View: Hadron Experimental Hall Baryons in Nuclei Mesons in Nuclei Beam Dump （ Movable on the Rail) 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 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) Energy Resolution (%,  /E)

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 radiator 99.9%

CsI Read-out