1. Solar Neutrinos in Super-Kamiokande ICHEP2014 @Valencia July 4 2014
Hiroyuki Sekiya
ICRR, University of Tokyo
for the Super-K Collaboration 1

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

3. Solar neutrinos observation
Super-K
n + e-  n + e-
3,4はいらないな。。この会議では。。 ne
Solar neutrinos observation

4. The results: Solar global fit
This SK update and other latest results are combined.
Combined solar fit with KamLAND
Without reactor θ13 constraint
Solar
KamLAND
Solar+KamLAND
Reactor
preliminary
sin2θ13=0.0242±0.0026
KamLAND
Solar+KamLAND
Solar
I would like to show the results at first
~2σ tension in Δm221
between solar and KamLAND
Non-zero q13 at 2s from solar+KamLAND
Good agreement with
Daya Bay, RENO & DC (Neutrino2014)
sin2θ13=0.0221±0.0012

5. Regenerate ne by earth matter effect
Motivation
Search for the direct signals of the MSW effect
Solar matter effect
Energy spectrum distortion
Earth matter effect
Flux day-night asymmetry
Neutrino survival probability
Regenerate ne by earth matter effect
JHEP 0311:004(2003)
Vacuum oscillation dominant
Solar+KamLAND
sin2θ12=0.308
Δm221=7.50x10-5eV2
up-turn!
Solar
sin2θ12=0.311
Δm221=4.85x10-5eV2
Matter oscillation
dominant

6. Improvements in SK-IV SK-III SK-IV New analysis in low energy bins
Reduced 222Rn BG
New analysis in low energy bins
Remaining BG-electrons from 214Bi should have more multiple-scatterings than signal-electrons have: MSG
MeV bin
SK-III
SK-IV
MeV
MSG < 0.35
0.35<MSG<0.45
0.45<MSG
MeV
SK is 17 years old, but sill improving
Reduced systematic error
1.7% for flux cf. SK-I: 3.2% SK-III: 2.1%
Achieved 3.5 MeV(kin.) energy threshold
8.6s signal is observed with MSG

7. 8B solar n in SK-I+II+III+IV
8B n signals
preliminary
FSK(8B) =2.344±0.034 x 106　cm-1s-1
FSK+SNO(8B)
= x 106　cm-1s-1
+0.17
-0.11
preliminary
~70k solar neutrino events
8B n could be the BG for DM search
through NC coherent scattering.

8. Recoil electron spectra
Data/MC(unoscillated)
preliminary
Kinetic energy (MeV)

9. SK-I+II+III+IV spectrum
N.B. All SK phase are combined without regard to energy resolution or systematics in this figure
(total # of bins of SKI - IV is 83) χ2
Solar+KamLAND
70.13
Solar
68.14
quadratic fit
67.67
exponential fit
66.54
Solar+KamLAND
sin2θ12=0.308 Δm221=7.50x10-5eV2
Solar
sin2θ12=0.311 Δm221=4.85x10-5eV2
Neutrino energy spectrum is convoluted in the electron recoil spectrum. For de-convolution, generic functions are used as a survival probability;
f8B=5.25 x 106/(cm2∙sec) fhep=7.88 x 103/(cm2∙sec)
SK recoil electron spectrum constrain the fit parameters (ci,ei) of the function and the allowed Pee(En) is derived using the allowed (ci,ei).

10. Allowed Pee(En) for SK preliminary
Solar+KamLAND
sin2θ12=0.308
Δm221=7.50x10-5eV2 SK
Solar
sin2θ12=0.311
Δm221=4.85x10-5eV2
MSW (solar+KamLAND) is consistent at ~1.6σ
MSW (solar) fits better (at ~0.7σ)

11. Allowed Pee(En) for SK+SNO
preliminary
Solar+KamLAND
sin2θ12=0.308
Δm221=7.50x10-5eV2 SK
SK+SNO
SNO
Solar
sin2θ12=0.311
Δm221=4.85x10-5eV2
SK and SNO are complementary for the shape constraint
MSW is consistent at 1σ

12. Global view of Pee(En) preliminary all solar (pp) Borexino (pep)
Borexino (8B)
Borexino (7Be)
SK+SNO
we see somehow upturn curve, but the significance level is 1sigma
Homestake
+SK+SNO
(CNO)

13. Flux zenith angle distribution
SK-I - IV combined (Eth=4.5 MeV for SK-I,III,IV MeV for SK-II)
Solar best fit
sin2θ12=0.311
Δm221=4.85x10-5eV2
Earth θz
Solar+KamLAND
sin2θ12=0.308
Δm221=7.50x10-5eV2
Sun
preliminary

14. Day/Night asymmetry amplitude
preliminary
Energy-dependence of the variation
Rate/Rateaverage
expected
Δm221=4.84x10-5 eV2
sin2θ12=0.311 sin2θ13=0.025
Fitted asymmetry amplitude
Δm221=4.84x10-5 eV2
Δm221=7.50x10-5 eV2
SK-I
-2.0±1.8±1.0%
-1.9±1.7±1.0%
SK-II
-4.4±3.8±1.0%
-4.4±3.6±1.0%
SK-III
-4.2±2.7±0.7%
-3.8±2.6±0.7%
SK-IV
-3.6±1.6±0.6%
-3.3±1.5±0.6%
combined
-3.3±1.0±0.5%
-3.1±1.0±0.5%
non-zero significance
3.0σ
2.8σ
First observation of day/night asymmetry
at 3s significance level

15. Δm221 dependence Solar region KamLAND region preliminary
sin2θ12=0.311, sin2θ13=0.025
1σ Solar
1σ KamLAND
Solar region
differ from zero
by 2.9~3.0σ
agree with expect
by 1.0σ
3.0σ
2.9σ
2.8σ
expected
SK-I,II,III,IV best fit
KamLAND region
differ from zero
by more than 2.8σ
agree with expect
by 1.3σ
Let me explain More precisely

16. Summary
SK has observed ~70000 solar n interactions, by far the largest sample of solar neutrino events in the world.
SK data provide the first indication (at 2.8~3.0 s) of terrestrial matter effects on 8B solar n oscillation.
SK gives the world’s strongest constraints on the shape of the survival probability Pee(Eν) in the transition region between vacuum oscillations and MSW resonance.
SK spectrum results are consistent with MSW up-turn prediction within ~1s.
SK measurements strongly constrain neutrino oscillation parameters:
SK gives world’s best constraint on Δm212 using neutrinos.
There is a 2s tension between SK’s neutrino and KamLAND’s anti- neutrino measurement of Δm212.
Last month SK started taking data at ~2.5 MeV at ~100% trigger efficiency. Stay tuned for very low energy SK neutrino.

17. Extra slides

18. Full summary
SK has observed ~70000 solar neutrino interactions in ~4500days (1.5 solar cycles), by far the largest sample of solar neutrino events in the world.
SK data provide the first indication (at 2.8~3.0 sigma) of terrestrial matter effects on 8B solar neutrino oscillation. This is the first observation using a single detector and identical neutrino beams that matter affects neutrino oscillations.
SK has successfully lowered the analysis threshold to ~3.5 MeV kinetic recoil electron energy.
SK gives the world’s strongest constraints on the shape of the survival probability Pee(Eν) in the transition region between vacuum oscillations and MSW resonance.
SK spectrum results slightly disfavor the MSW resonance curves, but are consistent with MSW prediction within sigma.
SK measurements strongly constrain neutrino oscillation parameters:
SK uniquely selects the Large Mixing Angle MSW region by >3sigma,
gives world’s best constraint on solar Δm2 using neutrinos,
and significantly contributes to the measurement of the solar angle.
There is a 2 sigma tension between SK’s neutrino and KamLAND’s anti-neutrino measurement of the solar Δm2.
Last month SK started taking data at ~2.5 MeV at ~100% trigger efficiency. Stay tuned for very low energy SK solar neutrino

19. Wide-band Intelligent Trigger
Reconstruction and Reduction just after Front-end
100% trigger efficiency above 2.5MeV(kin.)
Just started

20. Oscillation parameter

22. Event rate becomes low and stable in SK-IV
Improvements in SK-IV
Reduced BG
Event rate becomes low and stable in SK-IV
MeV bin
SK-III
SK-IV
Reduced systematic error
1.7% for flux cf. SK-I: 3.2% SK-III: 2.1%
SK is 17 years old, but sill improving
achieved 3.5 MeV(kin.) energy threshold
7.5s level signal is observed at 3.5MeV bin

23. significance of the signal
The MSG non-zero signal significance is 8.6 sigma (2.4129/0.2811)
MeV Data/SSM= Flux=

24. SK+SNO 8B total flux
For each oscillation parameter set there is a minimum chi2 and a 8B error term describing the parabolic increase of the chi2 with deviations from the best chi2. The reduced chi2 vs. 8B flux is below. The jump is due to the relatively coarse grid in theta12.
x10^6/(cm2 sec), which is a (+3%,-2%) error on the total 8B for SK+SNO compared to the 1.5% error of SK's ES flux by itself.

25. Systematic errors Total 1.7 % Source SK-IV flux (3.5-19.5MeV)
SK-III flux
( MeV)
energy scale
+1.14, -1.16%
±1.4%
energy resolution
+0.14, -0.08%
±0.2%
B8 spectrum
+0.33, -0.37%
trigger efficiency
±0.1%
±0.5%
angular resolution
+0.32, -0.25%
±0.67%
vertex shift
±0.18%
±0.54%
BG event cut
±0.36%
±0.4%
hit pattern cut
±0.27%
±0.25%
another vertex cut
removed
±0.45%
spallation cut
gamma cut
±0.26%
cluster hit cut
+0.45, -0.44%
BG shape
signal extraction
±0.7%
cross section
Systematic errors
Total 1.7 %

26. 8B solar n in SK-I+II+III+IV
8B n signals

27. Data set for global solar analysis
The most up-to-date data are used
SK:
SK-I 1496 days, spectrum MeV(kin.)+D/N:Ekin>4.5 MeV
SK-II 791 days, spectrum MeV(kin.)+D/N: Ekin>7.0 MeV
SK-III 548 days, spectrum MeV(kin.)+D/N: Ekin>4.5 MeV
SK-IV 1669 days, spectrum MeV(kin.)+D/N: Ekin>4.5 MeV
SNO:
Parameterized analysis (c0, c1, c2, a0, a1) of all SNO phased. (PRC88, (2013))
Same method is applied to both SK and SNO with a0 and a1 to LMA expectation
Radiochemical: Cl, Ga
Ga rate: 66.1±3.1 SNU (All Ga global) (PRC80, (2009))
Cl rate: 2.56±0.23 SNU(Astrophys. J.496, 505 (1998) )
Borexino: Latest 7Be flux (PRL 107, (2011))
KamLAND reactor : Latest (3-flavor) analysis (PRD88, 3, (2013))
8B spectrum: Winter 2006 (PRC73, 73, (2006))
8B and hep flux
f8B=5.25 x 106/(cm2∙sec) fhep=7.88 x 103/(cm2∙sec)

28. Day/Night Amplitude fit Straight calc. combined -3.3±1.0±0.5%
(sin2θ12=0.311, sin2θ13=0.025)
Amplitude fit
Straight calc.
(D-N)/((D+N)/2)
Δm221=4.84x10-5 eV2
Δm221=7.50x10-5 eV2
SK-I
-2.0±1.8±1.0%
-1.9±1.7±1.0%
-2.1±2.0±1.3%
SK-II
-4.4±3.8±1.0%
-4.4±3.6±1.0%
-5.5±4.2±3.7%
SK-III
-4.2±2.7±0.7%
-3.8±2.6±0.7%
-5.9±3.2±1.3%
SK-IV
-3.6±1.6±0.6%
-3.3±1.5±0.6%
-4.9±1.8±1.4%
combined
-3.3±1.0±0.5%
-3.1±1.0±0.5%
-4.1±1.2±0.8%
non-zero significance
3.0σ
2.8σ
preliminary
expected time variation as a function of cosθz
Rate/Rateaverage
α : day-night asym. scaling factor

29. exponential parameterization
Solar+KamLAND
sin2θ12=0.308
Δm221=7.50x10-5eV2
Solar
sin2θ12=0.311
Δm221=4.85x10-5eV2
SK spectrum, red : exponential, green : quadratic
preliminary

30. SK-I+II+III+IV spectrum
N.B. All SK phase are combined without regard to energy resolution or systematics in this figure
(total # of bins of SKI - IV is 83) χ2
Solar+KamLAND
70.13
Solar
68.14
quadratic fit
67.67
Solar+KamLAND
sin2θ12=0.308 Δm221=7.50x10-5eV2
Solar
sin2θ12=0.311 Δm221=4.85x10-5eV2
Neutrino energy spectrum is convoluted in the electron recoil spectrum. For de-convolution, a generic quadratic function is used as a survival probability;
f8B=5.25 x 106/(cm2∙sec) fhep=7.88 x 103/(cm2∙sec)
SK recoil electron spectrum constrain the fit parameters (ci) of the function and the allowed Pee(En) is derived using the allowed (ci).

31. Multiple scattering goodness
MeV
Induced multiple scattering goodness(MSG) in SK-IV analysis.
Although the 214Bi decay-electrons (majority of low energy BG) fluctuate up above 5.0MeV, they truly have energy less than 3.3MeV and should have more multiple scattering than true 5.0MeV electrons.
MSG > 0.45
MSG < 0.35
MeV
MSG > 0.45
MSG < 0.35

32. MSG
For each PMT hit pair, 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

33. Comparison with others
BOREXINO
SNO
KamLAND
Super-K
Comparing to other experiments, Super-K spectrum has the most precise results.
Super-K spectrum is the most precise!

34. Solar Neutrinos BOREXINO MSW (solar&KL) MSW (solar) BORE- XINO
Pee
p+p➝d+e++νe
(99.77%)
p+e-+p➝d+νe
(0.23%)
all solar
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
7Be+e-➝7Li+νe 99.9% 8B
7Be
7Be+p➝8B+γ 0.1%
Hep
8B+➝8Be*+e++νe
7Li+p➝α+α; 8Be*➝α+α

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

36. Convection suppression in SK
Very precisely temperature-controlled (±0.01oC) water is supplied to the bottom.
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