1. Future SK Program for e Physics Atsuko Kibayashi For the Super-Kamiokande Collaboration Okayama University June 14, 2013 1 RENO ５０ 2013/6/14

2. MOTIVATIONS 2013/6/14 RENO ５０ 2

3. 8 MeV ΔT~20μs Vertices within 50cm γ p n Gd e + e Captures on Gd Gd in Water 0.0001% 0.001% 0.01% 0.1% 1% 100% 80% 60% 40% 20% 0% 2013/6/143 RENO ５０ Neutron Capture by Gadolinium Large cross section of Gd for neutron capture – ~49,000 barns (0.3 barns on free proton) Coincident signal detection to suppress background Beacom and Vagins, Phys. Rev. Lett., 93:171101, 2004] 0.1% Gd gives 90% neutron capture eff. ~100 ton of Gd 2 (SO 4 ) 3 in SK

4. Physics of e by GADZOOKS! Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super! Observation of Supernova Relic Neutrino (SRN) – SRN has not yet been observed Supernova Burst Neutrinos – Better direction determination by enhancement of electron scattering events Reactor Neutrinos – Precise measurements of oscillation parameters by high statistics 2013/6/14 RENO ５０ 4

5. SRN Spectrum 2013/6/14 RENO ５０ 5 Expected SRN Spectrum ( e fluxes) SRN flux calculations Horiuchi st al. PRD, 79, 083013 (2009) Expected no. of SRN events 1.3-6.7 events/year/22.5kton (10-30MeV) Need: - Large target mass - Background removability

6. Expected SRN Signal and Background Assume : 90 % neutron capture efficiency, 74% Gd gamma detection efficiency, invisible muon B.G. is 35% of the SK-IV invisible muon B.G. Expect: 10-45 SRN events in 10-years data taking (Evis = 10- 30 MeV) 2013/6/146 RENO ５０

7. SN at 10kpc e +p +e Supernova Burst Direction w/o Neutron Tagging Neutrino flux and spectrum from Livermore simulation 2013/6/147 RENO ５０

8. SN at 10kpc e +p +e Supernova Burst Direction w/ Neutron Tagging Removing tagged events Neutrino flux and spectrum from Livermore simulation 2013/6/148 RENO ５０

9. SN Direction Determination Precision 2x better precision with neutron tagging. Direction Determination Precision (1000 MC events) tag eff. = 1.0 tag eff. = 0.8 tag eff. = 0.0 Number of supernovae 振動なし 振動あり（正階層性） 振動あり（逆階層性） Direction Determination Precision No Osc. Oscillated (normal hierarchy) Oscillated (inverted hierarchy) 2013/6/149 RENO ５０ H. Ishino

10. Questions Gd in SK? Water transparency? How to purify Gd water? How to introduce/remove Gd? Effect on SK material? Effect on solar neutrino analysis? In a water Cherenkov detector? 2013/6/14 RENO ５０ 10 EGADS

11. R&D 2013/6/14 RENO ５０ 11

12. SK water purification system ５０ｍ Super-Kamiokande To Atotsu entrance EGADS hall Parking place Underground site map 2013/6/1412 RENO ５０ EGADS Evaluating Gadolinium’s Action on Detector Systems

13. Gd-water filtration Gd purification (resin to remove U keeping Gd) Gd purification (resin to remove U keeping Gd) 200 m 3 SUS tank Transparency measuring device 13 EGADS Lab. in Kamioka Mine 2013/6/14 RENO ５０ 15 m 3 plastic tank (for dissolving Gd) 15 m 3 plastic tank (for dissolving Gd) Gd Removing Resin Feb.16, 2011

14. Water Monovalent Multivalent Viruses Bacteria Suspended Ions Ions Solids Water Monovalent Multivalent Viruses Bacteria Suspended Ions Ions Solids Water Monovalent Multivalent Viruses Bacteria Suspended Ions Ions Solids Water Monovalent Multivalent Viruses Bacteria Suspended Ions Ions Solids Microfiltration 1,000 – 100,000 angstroms membrane pore size Ultrafiltration 100 – 1,000 angstroms membrane pore size Nanofiltration 10 – 100 angstroms membrane pore size Reverse Osmosis 5 – 15 angstroms membrane pore size size Membrane filter technology smalllarge Gd 2 (SO 4 ) 3 M. Vagins

15. 200 ton EGADS Main Tank EGADS Selective Filtration System Intake Pump (>4 ton/hr) 5  m 1 st Stage Filter Concentrated Gd NF Reject Lines UV #1 Membrane Degas 0.2  m 2 nd Stage Filter 0.5 ton Collection Buffer Tank Repressurization Pump (>0.6 MPa, >4 ton/hr) Repressurization Pump (>0.6 MPa, >3 ton/hr) Nanofilter #2 Nanofilter #1 Ultrafilter #1 Repressur- ization Pump (>0.9 MPa, >2 ton/hr) TOC 5  m Filter 0.5 ton Buffer Tank RO #1 Ultrafilter #1 Ultrafilter #2 Repressurization Pump (>0.9 MPa, >1.5 ton/hr) DI #2 5  m Filter RO #2 RO Permeate Lines Conveying Pump (~0.35 MPa, >4 ton/hr) Recycles RO Reject Lines Chiller UF#1 Reject Line UF#2 Reject UV #2 DI #1 To Drain Nanofilter #1 Nanofilter #2 Ultrafilter #2 2013/6/1415 RENO ５０ M. Vagins

16. EGADS (Step 1) 200 m 3 tank Gd-water filtration system w/o PMT Circulation of pure water in 200 m 3 tank, to evaluate basic performance of the filtration system March – June, 2011 15m 3 tank

17. w/o PMT Circulation of 0.2% Gd 2 (SO 4 ) 3 dissolved water in15m 3 tank through the filtration system Measurement of Gd-dissolved water transparency August, 2011 – December, 2012 EGADS (Step 2) 200 m 3 tank Gd-water filtration system 15m 3 tank

18. w/o PMT EGADS (Step 3) 200 m 3 tank Gd-water filtration system 15m 3 tank Circulation of 0.2% Gd 2 (SO 4 ) 3 dissolved water in 200m 3 tank through the filtration system. Study of effects on SUS tank (accelerated studies have shown no problems) December, 2012 – June, 2013

19. Water Transparency Measurement Method 2013/6/14 RENO ５０ 19 T. Yano

20. SK-III and SK-IV Ultrapure Water = 74.7% - 82.1% @ 15 m 30 kg of Gd 2 (SO 4 ) 3 *8H 2 O  35% n capture on Gd 60 kg of Gd 2 (SO 4 ) 3 *8H 2 O  52% n capture on Gd89.4 kg of Gd 2 (SO 4 ) 3 *8H 2 O  62% on Gd149.4 kg of Gd 2 (SO 4 ) 3 *8H 2 O  73% on Gd274 kg of Gd 2 (SO 4 ) 3 *8H 2 O  83% on Gd400 kg of Gd 2 (SO 4 ) 3 *8H 2 O  88% on Gd 70 % => 85% of pure water 70 % => 85% of pure water 2013/6/1420 RENO ５０ M. Vagins Light Remaining at 15 m in 200 ton tank

21. 240 PMT mounting July - August, 2013 EGADS (Step 4) 200 m 3 tank Gd-water filtration system 15m 3 tank

22. Circulation of pure water, then 0.2% Gd 2 (SO 4 ) 3 dissolved water Integrated test Starting September, 2013 Mini-SK (w/ same SK material) EGADS (last Step) 200 m 3 tank Gd-water filtration system 15m 3 tank

23. GADZOOKS! for 2013/6/14 RENO ５０ 23

24. Effect on Solar Neutrino Analysis? To achieve 3.5 MeV(Kin.) solar neutrino analysis in 0.2% Gd+H2O SK, the following radioactivity levels would be needed. < 2.8 x 10 -11 g( 238 U)/g(Gd) < 8.6 x 10 -11 g( 232 Th)/g(Gd) < 9.6 x 10 -18 g( 226 Ra)/g(Gd) => Corresponds to < 0.35 mBq/kg(Gd) 2013/6/14 RENO ５０ 24 M. Smy

25. Radioactivity of Gd 2 (SO 4 ) 3 Radioactivity in Gd 2 (SO 4 ) 3 batches measured in Canfranc [mBq/Kg, limits are @ 95% c.l.] Chain Longest lived parent in sub-chain Product 1Product 2Product 3Product 4Product 5 238 U 51 ± 21< 33 292± 6774 ± 28242± 60 226 Ra8 ± 12,8 ± 0,674± 213± 113 ± 2 232 Th 228 Ra11 ± 2270 ± 16(*) 1099± 12205 ± 621 ± 3 228 Th29 ± 386 ± 5504± 6127 ± 3374 ± 6 235 U < 32 < 112< 25 227 Ac/ 227 Th214 ± 101700 ± 202956 ± 301423 ± 211750 ± 42 Others 40 K29 ± 512 ± 3 (*)101 ± 1060 ± 718 ± 8 138 La8 ± 1<683 ± 153 ± 142 ± 3 176 Lu80 ± 821 ± 2566 ± 612 ± 18 ± 2 Still too high 252013/6/14 RENO ５０ L. Labarga => To reduce Radium, one solution is to use commercial selective resins available.

26. Answers Gd in SK? Water transparency? How to purify Gd water? How to introduce/remove Gd? Effect on SK material? Effect on solar neutrino analysis? In a water Cherenkov detector? 2013/6/14 RENO ５０ 26 85% of pure water Method being established Mass removal still under study, commercial resin available Mass removal still under study, commercial resin available Gd 2 (SO 4 ) 3 proven to be safe Radioactivity still too high (esp. Ra). Commercial resin will be tested. Demonstration of Cherenkov detection of Gd(n, gamma) Gd (H.Watanabe et al. Astropart. Phys., 31, 320-328 (2009) Demonstration of Cherenkov detection of Gd(n, gamma) Gd (H.Watanabe et al. Astropart. Phys., 31, 320-328 (2009)

27. R&D Schedule 2013/6/14 RENO ５０ 27 M. Nakahata

28. Conclusion For SRN detection – A large target volume is needed => SK is the only one w/ that kind of volume – Addition of Gd unable us to detect SRN For SN detection – Direction accuracy can be improved by tagging e events 2013/6/14 RENO ５０ 28 Gd in water Cherenkov detector R&D project (EGADS) is in progress. Gd in SK looks more and more promising. We hope to start GADZOOKS! in a few years. As soon as EGADS successfully demonstrates the feasibility for GADZOOKS!, schedule for GADZOOKS! will be discussed among the SK collaboration.

29. BACKUPS 2013/6/14 RENO ５０ 29

30. EGADS Members ICRR, University of Tokyo – Y. Kishimoto, M. Nakahata, H. Sekiya Kavli, IPMU – L. Marti, M. Vagins Kobe University – Y. Takeuchi Okayama University – H. Ishino, A. Kibayashi, Y. Koshio, T. Mori, M. Sakuda, Y. Yamada, T. Yano, University Autonoma Madrid – L. Labarga, P. Fernadez University of California, Irvine – G. Carminati, J. Griskevich, B. Kropp, A. Renshaw, M. Smy, P. Weather 2013/6/14 RENO ５０ 30

31. UltrafilterNanofilter RO RO reject (processed in another loop) pure water (RO pass) and Gd 2 (SO 4 ) 3 Return to tank Water with Gd 2 (SO 4 ) 3 from the tank Gd 2 (SO 4 ) 3 (NF reject) Concept of the water circulation system Gd 2 (SO 4 ) 3 and UF passed water (UF pass) Small size contaminants (NF pass) Reject large size contaminants (UF reject) 31

32. Reactor Neutrino at GADZSOOKS! w/o oscillation w/ oscillation MeV With / without oscillation 10 years’ sensitivity sin 2 (2 θ) Δ m 2 (10 -4 eV) Number of events at SK per year （ ~ ３０００ /year ） Current solar+KamLAND error size Sensitivity of parameter measurement （ 10 years ） very preliminary ９５％ＣＬ

33. 400 kg  88% 274 kg  83% 149.4 kg  73% 89.4 kg  62% 60 kg  52% 30 kg of Gd 2 (SO 4 ) 3 8H 2 O in 200 tons  35% capture on gadolinium Captures on Gd Gd in Water 0.0001% 0.001% 0.01% 0.1% 1% 100% 80% 60% 40% 20% 0% Thermal neutron capture cross section (barns) Gd = 49700 S = 0.53 H = 0.33 O = 0.0002 2013/6/1433 RENO ５０ M. Vagins

34. [Yano-san] 2013/6/1434 RENO ５０

35. [Yano-san] 2013/6/1435 RENO ５０

36. [Yano-san] 2013/6/1436 RENO ５０

37. Gd Recovery System R&D at UCI 2013/6/14 RENO ５０ 37

38. Y. Takeuchi, ICRR M.Smy, “Low Energy Requirements for the GADZOOKS! Project”, SK meeting, Dec.3, 2006 382013/6/14 RENO ５０

39. Epoxy Test paint on welded part of the SUS tank BIO-SEAL 197BIO-DUR 560 39 M20 bolts in a flange apply epoxy w/o welding. Epoxy paints on the base of bolt. 2013/6/14 RENO ５０

40. Epoxy Test Pressure vessel The test flanges are put on both sides and give pressure to the vessel. Pressure test (0  5kg/cm 2 ) was done on Oct.19, 2011.  No leak and no pressure drop. Pressure cycle (0  5kg/cm 2 ) test was done on Oct.20-27.  No leak and no pressure drop. Long term stability test is running from Oct.28 for 3 months and no problem was found. Successful 40 2013/6/14 RENO ５０

41. Possibility of Acrylic Vessel additional layer of protection Basic idea: extend the frame above the PMTs and put thin acrylic plates. Outer detector Inner detector Acrylic vessel Gd-loaded water 412013/6/14 RENO ５０

42. This apparatus deployed in the SK tank. BGO 13 cm 18 cm 5 cm BGO 0.2 % GdCl 3 Solution Am/Be GdCl 3 test vessel Test Cherenkov emission of Gd(n,  )Gd α + 9 Be → 12 C * + n 12 C* → 12 C +  (4.4 MeV) n + p → …… → n + Gd → Gd +  (totally 8 MeV) BGO signal (prompt signal (large and long time pulse)) Look for Cherenkov signal (delayed signal)

43. Cherenkov signal of Gd gamma rays 0 Time from prompt 100  s Vertex position 92% within 2m dR [cm] Energy spectrum Measured time, vertex and energy distributions are as expected from the MC simulation. Astropart. Phys. 31, 320-328 (2009) arXiv:0811.0735