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Hiroyuki Sekiya ICRR, University of Tokyo for the Super-K Collaboration

S uper- K amiokande Low Energy Results -Solar neutrinos & SN neutrinos- NOW2012 @ Conca Specchiulla 14 September . Hiroyuki Sekiya ICRR, University of Tokyo for the Super-K Collaboration. 1. Super- Kamiokande. Physics targets of Super- Kamiokande. Proton decay. Relic SN ν. WIMPs.

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Hiroyuki Sekiya ICRR, University of Tokyo for the Super-K Collaboration

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  1. Super-KamiokandeLow Energy Results-Solar neutrinos & SN neutrinos-NOW2012 @ConcaSpecchiulla14 September Hiroyuki Sekiya ICRR, University of Tokyo for the Super-K Collaboration 1

  2. Super-Kamiokande Physics targets of Super-Kamiokande Proton decay Relic SN ν WIMPs Atmospheric ν Solar ν TeV GeV MeV ~3.5 ~20 ~100 ~1 Low energy 2 50kton pure water Cherenkov detector 1km (2.7km w.e) underground in Kamioka 11129 50cm PMTs in Inner Detector 1885 20cm PMTs in Outer Detector

  3. Solar neutrinos observation ne+ e- → ne+ e- ne

  4. Current motivation • Check the direct signal of the MSW effect Solar matter effect Energy spectrum up-turn Earth matter effect Flux day/nigh asymmetry Neutrino survival probability Night>Day : about 2% level Matter oscillation dominant Vacuum oscillation dominant See this up-turn!

  5. New SK-IV results are added • First results from SK-IV (1069.3 days of data) Hardware improvement Software improvement • Better water quality control • Lowered threshold (~3.5MeV (kin.)) • Large statistics with lower backgrounds. • New electronics • Better timing determination • Better MC model of trigger efficiency. • Introduce multiple scattering goodness • Although the 214Bi decay-electrons (majority of low energy BG) fluctuate up above 5.0 MeV, they truly have energy <3.3 MeV and should have more multiple scattering than true 5.0 MeV electrons, and therefore a lower MSG • Reduced systematic error • 1.7% for flux cf. SK-I: 3.2% SK-III: 2.1%

  6. Lowered background Solar angular distribution 3.5~4.0MeV(kin.) Event rates 4.0-4.5MeV(kin.) SK-III SK-III event/day/kton SK-IV Stable low background level SK-IV 8B n signal 763+113-111 Clear Solar peak ~7σ level 3.5MeV threshold is achieved!

  7. Solar angle distributionswith MSG in low energy 3.5-4.0MeV 0.35<MSG<0.45 MSG < 0.35 0.45<MSG 4.0-4.5MeV

  8. Recoil electron spectrum SK-I spectrum SK-II spectrum stat.+uncor. syst. uncertainties DATA/Unoscillated MC energy correlated error New SK-IV spectrum SK-III spectrum

  9. Recoil electron spectrum Distortion due to E dependence of Oscillation survival probability dsm/dse SK-I,II,III,IV DATA/Unoscillated MC sin2θ13=0.025 • sin2θ12=0.304 , Δm2=7.41∙10-5eV2 • sin2θ12=0.314 , Δm2=4.8∙10-5eV2 • Flat probability • Flat prob., dσ ratio f8B=5.25×106/(cm2∙sec) fhep=7.88×103/(cm2∙sec) Unoscillatedshape is favored ~1.1 to 1.9 s

  10. Comparison with others SNO KamLAND Super-K BOREXINO Super-K spectrum is the most precise!

  11. Day-Night amplitude SK-I,II,III,IV Day-Night Asymmetry 20% 10% 0 -10% -20% -30% -40% Day-Night amplitude -2.8 ±1.1(stat) ±0.5(sys)% Non-zero @2.3σ level sin2θ12=0.314 Δm212=4.8∙10-5eV2

  12. Allowed oscillation parameter region from Day/Night data KamLAND 1σ SK Day/Night Amplitude1σ The best constraint of Dm212 among all solar neutrino measurements

  13. Neutrino oscillation analysis ne nm nt

  14. q13analysis Solar+KamLAND Best fit +0.017 -0.015 sin2θ13=0.030 5σ 4σ Constraint to the following oscillation analyses 3σ Solar Data Combined 2σ Consistent with reactor experiments (0.025) 1σ KamLAND Daya Bay/Reno

  15. (Dm2 ,q12) from Only Super-K 12 SK (Day/Night) picks best-fit solar Δm221 nflux constraint KamLAND f8B=(5.25±0.20) x 106/(cm2∙sec) 15

  16. (Dm2 ,q12) from all solar data KamLAND 16

  17. Search for SN relic neutrinos SN1987a Credit: X-ray: NASA/CXC/PSU/S.Park & D.Burrows.; Optical: NASA/STScI/CfA/P.Challis • Many SRN models that predict both the flux and the spectrum of anti-neutrino have been constructed. All of the core collapse supernovae that have exploded throughout the history of the Universe have released neutrinos, which should still be in existence.

  18. Super-K sensitivity K.Bays et al., Phys.Rev.D85, 052007 (2012) Current SK BG (spallation + solar n) Analysis threshold Model predictions Models are parameterized in Tnof Fermi-Dirac emission For LMA model Ando et al., (2005) Combined 90% C.L.: < 5.1 ev / yr / 22.5 ktons < 2.7 /cm2/s (>16 MeV) BG should be reduced 　　　　　　　　　～O(104) SK-I+II+III result is only factor 2 higher than models!

  19. Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super! GADZOOKS! Project Beacom and Vagins, PRL, 93:171101, 2004 • Neutron tag (signal) efficiency : 90% • Background reduction : 2x10-4 _ ne can be identified by the delayed coincidence technique • 0.2% Gadolinium sulfate in SK

  20. EGADS Evaluating Gadolinium’s Action on Detector Systems Done From Dec. Transparency measurement 240 PMTs Pre-treatment system Main water circulation system R&D items • Water purification with gadolinium sulfate • Keep water transparency with gadolinium sulfate • Effects on Super-K components/materials • Neutron background and its effects • Detection efficiency

  21. UDEAL 200ton tank 15ton tank for pre-treat Gd water Circulation system pre-treatment system 21

  22. Status PMTs are not mounted yet Selective filtrationsystem • uses a molecular size band-pass scheme to filter the water. • Confirmed • Gd-kept eff.> 99.9% • Aug.2011- Present Long term stability and quality check • 0.2% Gd-loaded water circulation (w/o 200t tank)

  23. Conclusion • Solar neutrino measurement in Super-K keeps improving. • lower threshold, lower BG, smaller errors, and larger statistics • No significant spectrum distortion. • Asymmetry in day/night flux @2.3σ, hint of non-zero? • Neutrino oscillation parameters are updated from global fit; • Δm212=7.44+0.2-0.19x10-5eV2, sin2θ12=0.304±0.013, sin2θ13=0.030+0.017-0.015 • Adding 0.2% Gadolinium sulfate to SK, SRN event rate is expected to be 0.8 – 5.0 events/year/22.5kt (10 – 30 MeV) • EGADS, the R&D project is ongoing. • Neutron tagging efficiency measurement with 200t test tank and 240 PMTs will be done.

  24. Extra slides

  25. Solar neutrinos observation Neutrino-electron elastic scattering n + e- → n + e- • Solar direction sensitive • Realtimemeasurements • Energy spectrum • day/night flux differences • Seasonal variation ne Nuclear fusion reaction deep inside the Sun 4p➔2He+2e++2νe

  26. Solar neutrino spectrum (Bahcall-Pena-Garay-Serenelli 2008) ±X％ is theoretical uncertainties 7Be, pep : integrated flux pp ±0.5% 7Be ±5.8% +15% 13N −14% Neutrino Flux (cm-2/sec/MeV) Super-Kamiokande target pep +16% 15O ±1.1% −15% +19% 17F 8B ±11.3% −17% 7B ±5.8% hep ±15.5% Neutrino energy (MeV)

  27. Total solar neutrino event best fit: 0.451±0.007 φ8B=5.25×106/(cm2∙sec) φhep=7.88×103/(cm2∙sec) • about 19,000 events more than from pure νe • small systematic uncertainty • rate is consistent between all the SK phases

  28. Allowed oscillation parameter region from Day/Night data KamLAND 1σ SK Day/Night Amplitude 1σ The best constraint of Dm212 among all solar neutrino measurements

  29. Day/Night amplitude fitsas a function of Δm2

  30. Day/Night variation we assumed this kind of zenith angle shape from the neutrino oscillation parameter, and fit to the data. Expected rate variation Earth “matter” model Day/Night Asym.: ADN=2(φD-φN)/(φD+φN) from Phys.Rev. D69 011104 (2004): Δm212=6.3∙10-5eV2

  31. Only SNO KamLAND

  32. Super-K + SNO allowed regions much smaller KamLAND

  33. (Dm2 ,q12) from Only Super-K 12 SK (Day/Night) picks best-fit solar Δm221 n flux free nflux constraint KamLAND f8B=(5.25±0.20) x 106/(cm2∙sec) 33

  34. MSG For each PMThitpair, the vectors to the Chrenkov ring cross points are the direction candidates MSG = vector sum of the candidates/ scalar sum of the candidates MSG of multiple scattering events should be small

  35. Super-K water transparency @ Cherenkov light wavelength Measured by decay e-e+ from cosmic m-m+ SK-IV SK-III Started automatic temperature control anti-correlated with Supply water temperature

  36. Convection suppression in SK 3.5MeV-4.5MeV Event distribution Temperature gradation in Z Return to Water system The difference is only 0.2 oC Purified Water supply r2 Very precisely temperature-controlled (±0.01oC) water is supplied to the bottom.

  37. Current SK situation Bacteria in low flow rate region OD top 12t/h ID,OD top OD bottom ID bottom 36t/h Emanated (from PMT/ FRP) and accumulated Radon 60t/h 12t/h Ver.14May 2012 Stagnation and top-bottom asymmetry.

  38. SRN models SK rate prediction Flux prediction • Cosmology(cosmic star formation history, initial mass function, Hubble expansion, etc) is establised,so we can simply parameterize with • neluminosity of typical supernova • Average ne energy →neTemp. (Fermi-Dirac emission) spectrum)

  39. BG Cherenkov angle distribution • Dominant BGs are atomosphericvevm CC • SK-I data/MC Signal+BGfitting

  40. To Drain Selective Filtering System UF#1 Reject Line Ultrafilter #1 Ultrafilter #1 Chiller 15 ton EGADS Test Tank UV #1 0.2 m 2nd Stage Filter Repressurization Pump (>0.6 MPa, >4 ton/hr) 5 m 1st Stage Filter Intake Pump (>4 ton/hr) 99.7% of Gd Membrane Degas UF#2 Reject Nanofilter #1 0.5 ton Collection Buffer Tank Concentrated Gd NF Reject Lines Conveying Pump (~0.35 MPa, >4 ton/hr) Ultrafilter #2 0.27% Recycles RO Reject Lines 0.3% UV #2 0.5 ton Buffer Tank Repressurization Pump (>0.6 MPa, >3 ton/hr) RO Permeate Lines 0.03% Nanofilter #2 TOC Repressur-ization Pump (>0.9 MPa, >2 ton/hr) DI #2 Repressurization Pump (>0.9 MPa, >1.5 ton/hr) 7 ℓ/min DI #1 RO #2 5 m Filter 5 m Filter RO #1

  41. Gd-loaded water transparency Cherenkov light left at 15m Light sources 6 wavelength PD Usual SK pure water quality Resin treatment Filter replacement Worst SK pure water quality used for physics analysis PD 0.2% Gd-loaded water is OK for Cherenkov detector

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