1. Current Status of E14 Experiment at J-PARC 정명신, 김용주 1, 우종관 1, 고재우 1, 임계엽 2, 김은주 3, 안정근 4, 이효상 5 한양대학교, 1 제주대학교, 2 KEK, 3 전북대학교, 4 부산대학교, 5 서울대학교

2. 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. Hanyang Univ. National Taiwan Univ. Yamagata Univ.

3. 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12 10 -13 10 -5 BR SM Step 1 Step 2 New Phyics KEK E391a

4. 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

5. 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/spill8.1x10 6 3.3x10 5 x30/sec Run time12 months2 monthsx6 Decay prob.4%2%x2 Acceptance3.6%1%x3.6 Sensitivity0.8x10 -11 1.1x10 -8 x1300

6. 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).

7. Beam plug Dipole magnet 1 st collimator （ 4m-long ） 2 nd collimator (4.5+0.5m) Photo in July, 2009 beam

8. Target : Ni or Pt Particles produced by the proton beams The beam line bends 16 degrees against proton beams at the target Components of Beam Line ―Two colliminators ―Sweeping magnets ―Beam plugs ―Photon(gamma) absorber Beam Line

9. Preparation status Beamline construction in 2009. Beam survey – Nov. 2009 to Feb 2010 – 6×10 11 ~ 2 ×10 12 protons/spill CsI-calorimeter construction in 2010. Completion of whole detector in 2011. First Physics Run in 2012.

10. 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)

11. Beam Profile Monitor PWO, CsI crystals

12. Overall beam shape is well reproduced by M.C. simulation. Beam Profile

13. 13 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. Present Setup of Spectormeters

14. Measurement of K L Yield by detecting K L       0

15. January ―Ni Target 9.1 ×10 15 p.o.t. (0.5kW) 7.3 ×10 15 p.o.t. (1kW) ―Pt Target 1.0 ×10 15 p.o.t. (1kW) February ―Ni Target 2.0 ×10 16 p.o.t. (1kW) 6.5 ×10 15 p.o.t. (1kW) 1.0 ×10 16 p.o.t. (1kW) ―Pt Target 2.0 ×10 16 p.o.t. (1kW) Data Taking Beam Condition On spill time(s) PeriodTarget Beam Intensity (kW) Design0.73.3Ni0.3 Present2.66.0Ni or Pt0.5 ~ 2.0

16. It corresponds to Proposal-yield x 2.3 (*MR DCCT normalization) Measurement ―Ni Target : 1.83 ×10 7 K L ’s/2 ×10 7 p.o.t ―Ni Target : 3.73 ×10 7 K L ’s/2 ×10 7 p.o.t Our proposal ―Ni Target : 8.1 ×10 6 K L ’s/2 ×10 7 p.o.t Results of K L Productions

17. Reconstructed Mass. Reconstructed K L Momentum Momentum Distribution of K L

18. 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.

19. Vacuum chamber PMT holder installation Stacking of CsI crystals CsI Calorimeter Construction

20. 2011.Feb.08 16:30 stackin g July 2010 October 2010: engineering run with 1800 crystals KOTO CsI calorimeter completed KTeV CsI calorimeter 2700 crystals dismantled by December 2008

21. Conclusion Beam survey – Measured the beam profile with hodoscopes – Reconstructed the K L momentum with CsI crystals and plastic scintillators – twice the K L yields compared to the proposal CsI Calorimeter – Construction is done – Be ready for beam test

22. Backup Slides

23. 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

24. 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)

25. ItemJ-PARC E14 KOTO KEK-E391a Primary proton energy 30 GeV12 GeV Proton intensity(/spill) 2x10 14 2.5x10 12 Spill-length/repetition0.7s / 3.3s2s / 4s Production targetCommon “T1” Pt rod Extraction angle16 deg. 4 deg. KL yield(/spill)8.1x10 6 3.3x10 5 Average P KL 2.1 GeV/c2.6 GeV/c n/K L ratio 6.5 45 Parameters of beam Momentum dist. of K L. Momentum dist. of Neutron p

26. 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     0 1.8 K L       0 0.4 K L   - e + 0.005 KL   negligible KL       0 negligible Neutron Interaction With Residual gas 0.04 At the CC02 0.01 At the C.V. negligible Accidental coin. 0.10 MC: K L   0