hiroyuki sekiya icrc2013 jul. 8 2013 @rio de janeiro, brazil solar neutrino analysis of...

Hiroyuki Sekiya ICRC2013 Jul. 8 2013 @Rio de Janeiro, Brazil

Solar Neutrino Analysis ofSuper-Kamiokande

ICRC2013 @Rio de Janeiro 8 July 2013

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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

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Low energy

WIMPs

Hiroyuki Sekiya ICRC2013 Jul. 8 2013 @Rio de Janeiro, Brazil 3

neSolar neutrinos observation

nx + e-

→ nx + e-


Current motivation

Vacuum oscillation dominant

Matter oscillation dominant

up-turn!

Check the direct signals of the MSW effect

Neutrino survival probability

Solar matter effectEnergy spectrum up-turn

Earth matter effectFlux day-night asymmetry

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New SK-IV results

◦ 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%

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SK-IV Hardware improvement

SK-IV Analysis improvement

Results from 1306.3 days of SK-IV data 237days

data added to

Neutrino2012 re

sults


Lowered backgroundEvent rates4.0-4.5MeV(kin.)

Stable low background level

Solar angular distribution 3.5~4.0MeV(kin.)

Clear Solar peak ~7.5σ level3.5MeV threshold is achieved!

even

t/day

/kto

n

SK-IVSK-III SK-III

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SK-IV


Solar angle distributionswith MSG in low energy

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3.5-4.0MeV

4.0-4.5MeV

MSG < 0.35 0.35<MSG<0.45

0.45<MSG


SK-IV energy spectrum

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Statistically combined spectrum

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

sin2θ12=0.304 , Δm2=7.45∙10-5eV2Solar global+ KamLAND best value

sin2θ12=0.314 , Δm2=4.84∙10-5eV2Solar global best fit value

Flat probability fit

Exponential fit for testing “upturn”

sin2θ13=0.025

SK-I,II,III,IV

“upturn” shape is favored ~1s, “flat” is disfavored ~1s

Distortion due to E dependence of1)Oscillation survival probability, 2) dsm/dse ,3) Systematic uncertainties

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Comparison with others

BOREXINO

SNO KamLAND

Super-K

Super-K spectrum is the most precise!

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Day/Night FluxZenith angle distribution

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cosqz = 1 L ～ 15 ㎞qz

cosqz= -1, L ～ 13000 ㎞

SK-I+II+III+IV

sin2θ12=0.314 , Δm2=4.8∙10-5eV2Solar global best fit valuesin2θ12=0.304 , Δm2=7.41∙10-5eV2

Solar global+ KamLAND best value


Day-Night Asymmetry

sin2θ12=0.314Δm212=4.84x10-5eV2

SK-I+II+III+IV energy distribution

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AsymmetrySK-I -2.0±1.7±1.0 %SK-II -4.3±3.8±1.0 %SK-III -4.3±2.7±0.7 %SK-IV -3.4±1.8±0.6 %Combined

-3.2±1.1±0.5 % (2.7 σ from zero)

First indication of

Earth matter effect!


Dependence of Asymmetry on Dm221

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Solar global

KamLAND


Neutrino oscillation analysis

ne

nmnt

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Allowed oscillation parameter region from only SKDm21

2 ,q12

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Blue: day/night only 2s regionGreen: day/night +spectrum 2s region

Red: Solar global+KamLAND

SK provides most precise Dm21

2

among solarmeasurements

f8B free fit


(Dm212 ,q12) from all solar data

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f8B=(5.25±0.20) x 106/(cm2∙sec)

Green: Solar global dashed only SK+SNO Blue: KamLANDRed: Solar global+KamLAND

KamLANDSolarData

Combined


q13 Analysis w/ Solar+KamLAND

3σ

1σ

2σ

KamLAND

SolarDataCombined

Daya Bay/Reno

Consistent with reactor experiments (0.0242±0.0026)

Solar+KamLANDBest fitsin2θ13=0.031

+0.017

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non-zerosignificance2 s

-0.015


ConclusionSolar 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; ◦Δm2

12=7.45x10-5eV2, sin2θ12=0.304+0.013-0.013,

sin2θ13=0.031+0.017-0.015

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Extra slides

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Hiroyuki Sekiya ICRC2013 Jul. 8 2013 @Rio de Janeiro, Brazil 20

ne

Solar neutrinos observation

• Solar direction sensitive• Realtime measurements

• Energy spectrum• day/night flux differences• Seasonal variation

Nuclear fusion reaction deep inside the Sun

4p➔2He+2e++2νe

Neutrino-electron elastic scatteringn + e- → n + e-


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%


contour (flux free)

DN (flux free)DN+SpecSolar+KamLAND

2s


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


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


ID bottomOD bottom

OD topID,OD top 12t/h

12t/h

36t/h

60t/h

Ver.14May 2012

Current SK situationStagnation and top-bottom asymmetry.

Emanated (from PMT/FRP) and accumulated Radon

Bacteria in low flow rate region

hiroyuki sekiya icrc2013 jul. 8 2013 @rio de janeiro, brazil solar neutrino analysis of...

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