Solar Neutrinos in S uper- K amiokande ICHEP2014 @Valencia July 4 2014

Hiroyuki Sekiya ICHEP2014 Jul. 4 2014 @Valencia, Spain

Solar Neutrinos inSuper-Kamiokande

ICHEP2014 @Valencia July 4 2014

1

Hiroyuki SekiyaICRR, University of Tokyo

for the Super-K Collaboration


50kton pure water Cherenkov detector

1km (2.7km w.e) underground in Kamioka

11129 50cm PMTs in Inner Detector1885 20cm PMTs in Outer Detector

~3.5 ~20 ~1

Solar ν

MeV

Relic SN ν

GeV TeV

Atmospheric ν

~100

Physics targets of Super-Kamiokande

Proton decay

Super-Kamiokande

2

WIMPs

Hiroyuki Sekiya ICHEP2014 Jul. 4 2014 @Valencia, Spain 3

neSolar neutrinos observation

Super-K

n + e- n + e-


The results: Solar global fit This SK update and other latest results are combined.

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~2σ tension in Δm221

between solar and KamLAND

Solar

KamLAND

Solar+KamLAND

Reactor

preliminary

Non-zero q13 at 2s from solar+KamLANDGood agreement with Daya Bay, RENO & DC (Neutrino2014)

Without reactor θ13 constraintCombined solar fit with KamLAND

sin2θ13=0.0242±0.0026

KamLANDSolar+KamLAND

Solar

sin2θ13=0.0221±0.0012


Motivation

Vacuum oscillation dominant

Matter oscillation dominant

up-turn!

Search for the direct signals of the MSW effect

Neutrino survival probability

Solar matter effectEnergy spectrum distortion

Earth matter effectFlux day-night asymmetry

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Solar+KamLANDsin2θ12=0.308Δm2

21=7.50x10-5eV2

sin2θ12=0.311Δm2

21=4.85x10-5eV2

Solar

Regenerate ne by earth matter effectJHEP 0311:004(2003)


Improvements in SK-IV Reduced 222Rn BG

6

SK-III SK-IV

Achieved 3.5 MeV(kin.) energy threshold 8.6s signal is observed with MSG

Reduced systematic error 1.7% for flux cf. SK-I: 3.2% SK-III: 2.1%

4.0-4.5 MeV bin

New analysis in low energy bins Remaining BG-electrons from 214Bi should have more multiple-scatterings than signal-electrons have: MSG

3.5-4.0MeV

4.0-4.5MeV

MSG < 0.35 0.35<MSG<0.45 0.45<MSG


8B solar n in SK-I+II+III+IV8B n signals

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~70k solar neutrino events

8B n could be the BG for DM searchthrough NC coherent scattering.

FSK(8B) =2.344±0.034 x 106 　 cm-1s-1

preliminary

FSK+SNO(8B) =5.30 x 106 　 cm-1s-1+0.17

-0.11

preliminary


Recoil electron spectra

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Dat

a/M

C(u

nosc

illat

ed)

preliminary

Kinetic energy (MeV)


SK-I+II+III+IV spectrum

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N.B. All SK phase are combined without regard to energy resolution or systematics in this figure

Neutrino energy spectrum is convoluted in the electron recoil spectrum. For de-convolution, generic functions are used as a survival probability;

Solar+KamLANDsin2θ12=0.308 Δm2

21=7.50x10-5eV2

Solarsin2θ12=0.311 Δm2

21=4.85x10-5eV2

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).

f8B=5.25 x 106/(cm2∙sec) fhep=7.88 x 103/(cm2∙sec)

(total # of bins of SKI - IV is 83) χ2

Solar+KamLAND 70.13Solar 68.14

quadratic fit 67.67exponential fit 66.54


Allowed Pee(En) for SK

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SK

Solar+KamLAND

Solar

✓MSW (solar+KamLAND) is consistent at ~1.6σ✓MSW (solar) fits better (at ~0.7σ)

sin2θ12=0.308Δm2

21=7.50x10-5eV2

sin2θ12=0.311Δm2

21=4.85x10-5eV2

preliminary


Allowed Pee(En) for SK+SNO

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SK+SNOSNO

SK

Solar+KamLAND

Solar

✓SK and SNO are complementary for the shape constraint✓MSW is consistent at 1σ

sin2θ12=0.308Δm2

21=7.50x10-5eV2

sin2θ12=0.311Δm2

21=4.85x10-5eV2

preliminary


Global view of Pee(En)

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SK+SNO

Borexino (8B)

all solar (pp) Borexino (pep)

Borexino (7Be)

Homestake+SK+SNO

(CNO)

preliminary


Earth

θz

Solar best fit

Solar+KamLAND

preliminary

SK-I - IV combined (Eth=4.5 MeV for SK-I,III,IV 6.5 MeV for SK-II)

sin2θ12=0.308Δm2

21=7.50x10-5eV2

sin2θ12=0.311Δm2

21=4.85x10-5eV2

Sun

Flux zenith angle distribution


Day/Night asymmetry amplitude

Fitted asymmetry amplitudeΔm221=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 2.8σ14

Rat

e/R

ate a

vera

ge

expected

preliminary

Δm221=4.84x10-5 eV2

sin2θ12=0.311 sin2θ13=0.025

Energy-dependence of the variation

First observation of day/night asymmetry at 3s significance level


Δm221 dependence

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sin2θ12=0.311, sin2θ13=0.0251σ KamLAND1σ Solar

SK-I,II,III,IV best fit

expected2.8σ2.9σ3.0σ

Solar regiondiffer from zero by 2.9~3.0σagree with expect by 1.0σ

differ from zero by more than 2.8σagree with expect by 1.3σ

KamLAND region

preliminary


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 Δm21

2. Last month SK started taking data at ~2.5 MeV at ~100% trigger

efficiency. Stay tuned for very low energy SK neutrino.

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Extra slides

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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 1-1.7 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

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Wide-band Intelligent Trigger Reconstruction and Reduction just after Front-end

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Just started

100% trigger efficiency above 2.5MeV(kin.)


Oscillation parameter

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Improvements in SK-IV Reduced BG

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SK-III SK-IV

achieved 3.5 MeV(kin.) energy threshold7.5s level signal is observed at 3.5MeV bin

Event rate becomes low and stable in SK-IV

Reduced systematic error 1.7% for flux cf. SK-I: 3.2% SK-III: 2.1%

4.0-4.5 MeV bin


significance of the signal

The MSG non-zero signal significance is 8.6 sigma (2.4129/0.2811)

3.5- 4.0 MeV Data/SSM=0.4596+0.0546-0.0535 Flux=2.4129+0.2866-0.2811

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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.

5.30+0.17-0.11x10^6/(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.

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Systematic errors

Total 1.7 %

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Source SK-IV flux(3.5-19.5MeV)

SK-III flux(4.5-19.5MeV)

energy scale +1.14, -1.16% ±1.4%energy resolution +0.14, -0.08% ±0.2%

B8 spectrum +0.33, -0.37% ±0.2%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 ±0.2% ±0.2%gamma cut ±0.26% ±0.25%

cluster hit cut +0.45, -0.44% ±0.5%BG shape ±0.1% ±0.1%

signal extraction ±0.7% ±0.7%cross section ±0.5% ±0.5%


8B solar n in SK-I+II+III+IV8B n signals

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Data set for global solar analysis

SK:◦ SK-I 1496 days, spectrum 4.5-19.5 MeV(kin.)+D/N:Ekin>4.5 MeV ◦ SK-II 791 days, spectrum 6.5-19.5 MeV(kin.)+D/N: Ekin>7.0 MeV◦ SK-III 548 days, spectrum 4.0-19.5 MeV(kin.)+D/N: Ekin>4.5 MeV◦ SK-IV 1669 days, spectrum 3.5-19.5 MeV(kin.)+D/N: Ekin>4.5 MeV

SNO:◦ Parameterized analysis (c0, c1, c2, a0, a1) of all SNO phased. (PRC88, 025501 (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, 015807 (2009))◦ Cl rate: 2.56±0.23 SNU(Astrophys. J.496, 505 (1998) )

Borexino: Latest 7Be flux (PRL 107, 141302 (2011)) KamLAND reactor : Latest (3-flavor) analysis (PRD88, 3, 033001 (2013)) 8B spectrum: Winter 2006 (PRC73, 73, 025503 (2006)) 8B and hep flux

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The most up-to-date data are used



Day/Night

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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 2.8σexpected time variation as a function of cosθz

preliminary

(sin2θ12=0.311, sin2θ13=0.025)R

ate/

Rat

e ave

rage

α : day-night asym. scaling factor


exponential parameterization

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preliminary✓SK spectrum, red : exponential, green : quadratic

Solar+KamLAND

Solar

sin2θ12=0.308Δm2

21=7.50x10-5eV2

sin2θ12=0.311Δm2

21=4.85x10-5eV2


SK-I+II+III+IV spectrum

30

(total # of bins of SKI - IV is 83) χ2

Solar+KamLAND 70.13Solar 68.14

quadratic fit 67.67

N.B. All SK phase are combined without regard to energy resolution or systematics in this figure

Neutrino energy spectrum is convoluted in the electron recoil spectrum. For de-convolution, a generic quadratic function is used as a survival probability;

Solar+KamLANDsin2θ12=0.308 Δm2

21=7.50x10-5eV2

Solarsin2θ12=0.311 Δm2

21=4.85x10-5eV2

SK recoil electron spectrum constrain the fit parameters (ci) of the function and the allowed Pee(En) is derived using the allowed (ci).



Multiple scattering goodnessInduced 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.

3.5-4.0MeV

4.0-4.5MeV

MSG < 0.35

MSG < 0.35

MSG > 0.45

MSG > 0.45

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MSG

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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


Comparison with others

BOREXINO

SNO KamLAND

Super-K

Super-K spectrum is the most precise!

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Solar Neutrinos

SK & SNO

BORE-XINO

Cl

all solar BOREXINOBORE-XINO

8B

pp

Hep

pep

Pee

7Be

MSW (solar&KL)MSW (solar)

p+p d+e➝ ++νe(99.77%)p+e-+p d+➝ νe(0.23%)

3He+p α+e➝ ++νe

d+p➝3He+γ

3Ηe+α➝7Be+γ 15.08%

7Be+p➝8B+γ 0.1%

8B+➝8Be*+e++νe

3Ηe+3Ηe α+2p➝ 84.92%

7Li+p α+α;➝ 8Be* α+α➝

7Be+e-➝7Li+νe 99.9%


Super-K water transparency

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anti-correlated with Supply water temperature

@ Cherenkov light wavelengthMeasured by decay e-e+ from cosmic m-m+

SK-IVSK-III

Started automatic temperature control


Convection suppression in SKVery precisely temperature-controlled

(±0.01oC) water is supplied to the bottom.

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3.5MeV-4.5MeVEvent distributionReturn to

Water system

PurifiedWater supply

r2

Temperature gradation in Z

The difference is only 0.2 oC

Documents

Solar Neutrinos in S uper- K amiokande ICHEP2014 @Valencia July 4 2014