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Solar Neutrino Analysis of S uper- K amiokande ICRC2013 @Rio de J aneiro 8 July 2013

Solar Neutrino Analysis of S uper- K amiokande ICRC2013 @Rio de J aneiro 8 July 2013 . 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. Atmospheric ν. Solar ν.

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Solar Neutrino Analysis of S uper- K amiokande ICRC2013 @Rio de J aneiro 8 July 2013

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  1. Solar Neutrino Analysis ofSuper-KamiokandeICRC2013 @Rio de Janeiro 8 July 2013 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 nx+ e- → nx+ e- ne

  4. Current motivation • Check the direct signals of the MSW effect Solar matter effect Energy spectrum up-turn Earth matter effect Flux day-night asymmetry Neutrino survival probability Vacuum oscillation dominant up-turn! Matter oscillation dominant

  5. New SK-IV results 237days data added to Neutrino2012 results • Results from 1306.3 days of SK-IV data SK-IV Hardware improvement SK-IV Analysis 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(MSG) • 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 Clear Solar peak ~7.5σ level 3.5MeV threshold is achieved!

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

  8. SK-IV energy spectrum

  9. SK-I,II,III,IV Statistically combined spectrum Distortion due to E dependence of 1)Oscillation survival probability, 2) dsm/dse,3) Systematic uncertainties sin2θ13=0.025 • sin2θ12=0.304 , Δm2=7.45∙10-5eV2 • Solar global+ KamLAND best value • sin2θ12=0.314 , Δm2=4.84∙10-5eV2 • Solar global best fit value • Exponential fit • for testing “upturn” f8B=5.25×106/(cm2∙sec) fhep=7.88×103/(cm2∙sec) • Flat probability fit “upturn” shape is favored ~1s, “flat” is disfavored ~1s

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

  11. SK-I+II+III+IV Day/Night Flux • sin2θ12=0.314 , Δm2=4.8∙10-5eV2 • Solar global best fit value • sin2θ12=0.304 , Δm2=7.41∙10-5eV2 • Solar global+ KamLAND best value cosqz= -1, L～13000㎞ cosqz = 1 L～15㎞ qz Zenith angle distribution

  12. Day-Night Asymmetry SK-I+II+III+IV energy distribution sin2θ12=0.314 Δm212=4.84x10-5eV2 First indication of Earth matter effect!

  13. Dependence of Asymmetry on Dm221 KamLAND Solar global

  14. Neutrino oscillation analysis ne nm nt

  15. Allowed oscillation parameter region from only SK • Blue: day/night only 2s region • Green: day/night • +spectrum 2s region • Red: Solar global+KamLAND SK provides most precise Dm212 among solar measurements f8B free fit Dm212 ,q12

  16. (Dm212 ,q12) from all solar data • Green: Solar global • dashed only SK+SNO • Blue: KamLAND • Red: Solar global+KamLAND Combined KamLAND Solar Data f8B=(5.25±0.20) x 106/(cm2∙sec) 16

  17. q13Analysis w/ Solar+KamLAND Solar+KamLAND Best fit +0.017 -0.015 sin2θ13=0.031 non-zero significance 2 s 3σ Solar Data Combined 2σ Consistent with reactor experiments (0.0242±0.0026) 1σ KamLAND Daya Bay/Reno

  18. Conclusion • Solar neutrino measurement in Super-K keeps improving. • lower threshold, lower BG, smaller errors, and larger statistics • “1 s significance” spectrum distortion. • Asymmetry in day/night flux! @2.7σ, • Confirmation of Earth matter effect on Solar neutrino! • Neutrino oscillation parameters are updated from solar + KamLAND global fit; • Δm212=7.45x10-5eV2, sin2θ12=0.304+0.013-0.013, sin2θ13=0.031+0.017-0.015

  19. Extra slides

  20. 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

  21. Solar Neutrinos Pee p+p➝d+e++νe (99.77%) all solar p+e-+p➝d+νe (0.23%) BOREXINO BORE- XINO pep pp MSW (solar&KL) d+p➝3He+γ MSW (solar) SK & SNO 3Ηe+α➝7Be+γ 15.08% 3Ηe+3Ηe➝α+2p 84.92% 3He+p➝α+e++νe Cl BORE- XINO 8B 7Be+e-➝7Li+νe99.9% 7Be 7Be+p➝8B+γ 0.1% Hep 8B+➝8Be*+e++νe 7Li+p➝α+α; 8Be*➝α+α

  22. contour (flux free) 2s DN (flux free) DN+Spec Solar+KamLAND

  23. 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

  24. 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

  25. 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.

  26. 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.

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