Super-Kamiokande

Recent neutrino oscillaon studies

Shoei Nakayama (Kamioka Observatory, ICRR)

February 13, 2015 HPNP2015 @ University of Toyama Fundamental quesons about neutrinos n Why neutrino masses are so ny? n Why neutrino mixing is so strong? n What the ordering of three neutrino masses is? n Whether the three-neutrino mixing violates the maer- anmaer (CP) symmetry? n Whether empirical relaonships between neutrino-mixing parameters (or between neutrino- and quark-mixing parameters) can be established? n Whether the three-neutrino mixing picture is the whole story? n … Neutrino experiments aim to answer these quesons.

2 Neutrino experiments : Broad physics programs o Oscillaon studies o Neutrino-nucleus n Atmospheric ν interacon measurements n Accelerator ν n Solar ν o Neutrino astronomy n Reactor ν n Supernovae burst ν n Relic ν (DSNB) o Exocs searches n Very high-E cosmic ν n Sterile ν n Indirect search for DM n Lorentz invariance violaon (WIMP annihilaon) n Solar flare ν o Neutrino properes n Cosmological ν n kinemac ν mass n 0ν double β decay o Neutrino geophysics

3 in Neutrino Oscillaon ParametersUnknowns

c = cos! , s = sin! CP phase ij ij ij ij ! 'i# $ ! ! $ ! $ c 0 s e ! c s 0 $! ! $ # e & # 1 0 0 &# 13 13 &# 12 12 &# 1 & # ! & = # 0 c s &# 0 1 0 &# 's c 0 &# ! & µ 23 23 # & 12 12 2 # & # & i# # &# & # ! & 0 's23 c23 # 's13e 0 c13 & 0 0 1 !3 " " % " %" %" %" %

o o Neutrino Mass Hierarchy • θ12 = 33.9 ± 1.0 Solar ν, KamLAND o o Normal OR Inverted • θ23 = 45 ± 6 (90%CL) Atm. ν, Acc. ν o 2 θ23 : How close to 45 ? ~7.6e-5 eV o o Octant? (<45 , >45 ?) ~2.4e-3 eV2 o o 8.7o ± 0.4o by Daya Bay • θ13 = 9.0 ± 0.5 PRD 90, 071101(R) (2014) ~2.4e-3 eV2 ~7.6e-5 eV2 First indicaon of θ13≠0 by T2K (2011)

Precise measurements by reactor ν experiments (2012- ) 4 Kamioka Observatory (ICRR, University of Tokyo)

We are here now n Located in Hida-City, Gifu prefecture n Established in 1995 to conduct the Super-Kamiokande experiment n Other experiments (XMASS, etc.) also in the Kamioka Underground Lab.

Mt. Ikeno-yama ~30km south 1369 m

Research Building

Entrance to the Kamioka Observatory underground lab. 5 Super-Kamiokande

o 50 kton Water Cherenkov detector

n 22.5 kton fiducial mass

o 1000 m (2700 m.w.e.) under the peak 41.4m of Mt. Ikeno-yama o Opcally separated into 39.3m ©Scienfic American n Inner detector : 11,146 50cmφ PMTs n Outer detector : 1,885 20cmφ PMTs o Serves as the far detector for LBL experiments n 250/295 km from KEK-Tsukuba/J-PARC (K2K/T2K)

Atmospheric ν ~3.5 MeV ~20 ~100 ~1 GeV TeV 6 History of Super-K

>18 years of observaon with connuous improvement

96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

SK-I SK-II SK-III SK-IV

!"#$%&"'()#*+,- 5678 .'/01'(23"4- 56788 567888 56789 !!!"#$%&$'()* 6!78$%&$'()* !!!89$%&$'()* :;1.<2/=>.* +",-$./0123415 +!9-$./0123415 +",-$./0123415 ?@423A1 7 Solar neutrino observaon in Super-K

The Sun

SK range ν

ν + e- à ν + e- n Detects recoil electrons by neutrino-electron elasc scaerings n Direcon relave to the Sun n Energy spectrum n Realme measurements Typical event n Day-Night flux difference

n Seasonal flux variaon 8 8B solar ν flux measurement : Latest SK results

SK-IV improvements

n BG reducon by beer water quality control à Achieved the 3.5 MeV (kin.) energy threshold ! n New mulple scaering “goodness” parameter n Reduced systemac error (1.7% for flux, cf. SK-I: 3.2%, SK-III: 2.1%) by NASA

25000 4505 days data (SK-I ~ IV) SK 8B ν flux

Events/bin 20000 ~70000 signal extracted! 15000 by far the largest sample of solar ν events in the world 10000 : Data 5000 : Best fit # of : Background Sunspots 0 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 coseSun ΦSK(8B) = 2.344 ± 0.034 [106/cm2/s] No correlaon with solar acvity 9 SK solar ν measurements : Current targets

Direct verificaon of maer (MSW) effects in neutrino oscillaons

Solar maer effect Earth maer effect

à “Upturn” in energy spectrum à Day-Night flux asymmetry

Survival probability

Regenerate νe by Earth maer effect Test of some exoc models (FCNC, sterile νs, MaVaNs, …) 10 Solar maer effect

Solar νe survival probability : Latest SK results

n SK gives the strongest constraints on the shape of survival

probability Pee(Eν) in the transion region (MSWàVacuum)

allowed region n Slightly disfavor the MSW curves, but are consistent with MSW ν energy in MeV predicon w/ 1-1.7σ n To see the spectrum upturn clearly, n Trying to further reduce the BG and enlarge the FV

n Installing an intelligent trigger w/ 100% efficiency for Ekin>2.5MeV 11 昼夜変動! ◆!"#*%&'()$+,#--.)/#$ !"#$ ●昼間と夜間における$ 太陽ニュートリノ&ůƵdž;ɎͿを比較$ 567$8$96:$;.<$

Earth maer effect PRL 112, 091805 (2014) %&'()$ 8 天頂$ 地表$ 地球の裏 Day-Night B ν flux asymmetry : Latest SK results◆物質効果によるニュートリノ振動$ $

012エネルギー$ Zenith angle distribuon of 8B ν flux (SK-I 質量差~ IV combined)૛ 032 ο࢓૛૚ $ !"#$ 042地球の密度$ 2.55 などに依存、 $

Day Night /sec] 2 これらを考慮して、$ 2.5 96:$8$196:$;.<$

$()'&% $を決めるۼcm ࡭۲/ 6 Night

10 2.45 × + Night "!

2.4 Day

Flux[ Solar best fit i 2 sin !12=0.311, 2 -5 2 2.35 "m 21=4.85x10 eV

2.3 Solar+KamLAND

B Solar 2 sin !12=0.308, 8 2 -5 2 Day "m 21=7.50x10 eV 2.25 Best fit 2 sin !12=0.311 2 -5 2 "m 21=4.17x10 eV -2ALL -1.5Day Night -1 -0.5 0 0.5 1 coseZenith First direct indicaon (~3σ) of terrestrial maer effect

12 Atmospheric neutrino observaon

n Cosmic rays strike air nuclei and the decay of the out-going hadrons gives neutrinos

n νs travel 10-13,000 km before detecon n Flux spans many decades in energy :

~100 MeV – 10 TeV+ n Excellent tool for broad studies of ν osc.

n Super-K : 4581 days of atm-ν data n 40,000 events n Access to sub-leading effects

13 Searching for three-flavor oscillaon effects

Sub-dominant oscillaon effects sensive to

n Mass hierarchy : Resonance in mul-GeV νe or νe n θ23 octant : Magnitude of the resonance 2 54n III PHYSICS POTENTIAL CP δ : Two Δm interference region

2 2 o 2 2 o cosΘν=-0.8 NH, sin θ =0.4, sin θ =0.025, δ=40 cosΘν=-0.8 NH, sin θ =0.6, sin θ =0.025, δ=40

flux 23 13 23 13

e 1 1

1 solar term

ν (a) (b) − 0.8 interference term 0.8 ) 13 e 0.6 θ resonance term 0.6 ν total θ23<45° or θ23>45° ( Normal

0 0.4 0.4

Ψ 0.2 0.2

)/ Hierarchy

e 0 ν 0 ν

( 順質量階層 -0.2 -0.2 2 Ψ = -0.8) -0.4 -0.4 Δm 23>0 -1 -1 10 1 10 10 1 10 zenith CP=40o or 220o

Θ 2 2 o 2 2 o cosΘν=-0.8 NH, sin θ =0.6, sin θ =0.025, δ=220 cosΘν=-0.8 IH, sin θ =0.6, sin θ =0.025, δ=40 1 23 13 1 23 13 1

cos (c) (d) −

( 0.8 0.8

) 逆質量階層 e 0.6 0.6 2 ν Δm 23<0 (

0 0.4 0.4

Ψ 0.2 0.2 )/

e 0 0 Inverted ν ( -0.2 -0.2 Hierarchy Ψ -0.4 -0.4 -1 -1 10 1 10 10 1 10 Fraconal change of upward Eν (GeV) Eν (GeV) 14 Eν(GeV) Eν(GeV)

FIG. 34. Oscillated νe flux relative to the non-oscillated flux as a function of neutrino energy for the upward-going neutrinos with zenith angle cos Θ = 0.8.ν ¯ is not included in the plots. Thin solid ν − e lines, dashed lines, and dotted lines correspond to the solar term, the interference term, and the θ13 resonance term, respectively (see Eq. 5). Thick solid lines are total fluxes. Parameters are set as 2 2 2 2 2 5 2 3 2 (sin θ , sin θ , sin θ , δ, ∆m , ∆m )=(0.31, 0.025, 0.6, 40◦, 7.6 10− eV , +2.4 10− eV ) unless oth- 12 13 23 21 32 × × 2 2 erwise noted. The θ23 octant effect can be seen by comparing (a) (sin θ23 =0.4) and (b) (sin θ23 =0.6). δ

value is changed to 220◦ in (c) to be compared with 40◦ in (b). The mass hierarchy is inverted only in (d)

so θ13 resonance (MSW) effect disappears in this plot. For the inverted hierarchy the MSW effect should

appear in theν ¯e flux, which is not shown in the plot.

2 happens with neutrinos in the case of normal mass hierarchy (∆m32 > 0), and with anti-neutrinos 2 in the case of inverted mass hierarchy (∆m32 < 0).

In order to demonstrate the behavior of these three terms, Fig. 34 shows how the νe flux changes as a function of neutrino energy based on a numerical calculation of oscillation probabilities, in which the matter density profile in the Earth is taken into account [25, 68]. We adopted an Earth model constructed by the median density in each of the dominant regions of the preliminary reference Earth model (PREM) [69]: inner core (0 r<1220km) 13.0 g/cm3, outer core (1220 ≤ ≤ r<3480km) 11.3 g/cm3, mantle (3480 r<5701km) 5.0 g/cm3, and the crust (5701 r< ≤ ≤ 3 6371km) 3.3 g/cm . In Fig. 34 dotted lines correspond to the θ13 resonance term (the third term in Eq. 5), which could make a significant contribution in the 5 10 GeV region if sin2 θ is a few ∼ 13 Parcle idenficaon (PID) in Super-K

νe CC νµ CC

Super Kamiokande IV 1417.4 days : Monitoring

e-like 3191 muon-like 3110 250 e-like µ-like Excellent PID between showering atmospheric200 ν data (e-like) and non-showering (µ-like)

MC CCQE electron CCQE muon 150 n Ring shape and opening angle 100 n < 1% mis-ID at 1 GeV 50

0 -10 -8 -6 -4 -2 0 2 4 6 8 10 PID likelihood sub-GeV 1ring (FC) 15 Super-K atmospheric ν analysis samples

Fully Contained (FC) Zenith angle distribuon of each sample

Partially Contained (PC)

Upward-going Muons (Up-µ) n In total 19 analysis samples (classified by ν flavors, event topologies, energies, …)

n Fit to the data in bins of cosΘzenith and momentum n Dominated by νµàντ oscillaons n Interested in sub-dominant contribuons n Three-flavor effects, Sterile Neutrinos, LIV, … 16 SK three-flavor oscillaon analysis results 1st octant 2nd octant CPC CPC CPC o o SK Preliminary θ23 < 45 θ23 > 45 Super-K Atm ν SK Preliminary T2K νµ Run1-4

) MINOS Beam+ Atm 2 Δχ2 Δχ2 Normal Hierarchy

(eV Inverted Hierarchy 32 2 m Δ

90% SK Preliminary 90% Normal Hierarchy

2 2 0 2π sin θ23 sin θ23 δCP 2 2 n Normal hierarchy is slightly preferred (χ IH - χ NH = 0.9) 2 n Best-fit sin θ23 is ~0.6, but both the octants sll allowed

n Best-fit δCP is ~3π/2, but CP conservaon (sinδ=0) sll allowed

n With constraints by T2K, the preference of NH and δCP~3π/2 is slightly strengthened, but not definive. 17 T2K (Tokai-to-Kamioka) experiment

T2K beam accumulaon history Intense ν beam J-PARC µ 30GeV 295km Main-Ring

Super-K Near Detectors

Primary goals

n Discovery of νe appearance (νµàνe oscillaons via non-zero θ13) Opens the possibility to probe the leptonic CP violaon

à Definive observaon at >7σ (2013) Achieved w/ only 8% of

approved beam stascs n Precision measurement of νµ disappearance

à θ23 measurement with the world-leading precision (2014) 18 arXiv:1502.01550

Latest T2K results : Joint νµ + νe analysis

) 2

ν sample eV

µ -3

Disappearance (10 32 2 m

120 observed Δ 446±23 un-osc. MC + Combined fit T2K RUN1-4 data Best fit signal ν sample ie e 10 Background component 2 sin θ23 candidate events

e

Appearancei 5 Δχ2 excluded Number of 28 observed 0 0 500 1000 at 90%CL 4.9±0.6 un-osc. MC Reconstructed neutrino energy (MeV)

IH n With a constraint on θ13 by reactor ν, excluded T2K data favors NH and δ ~-π/2. at 90%CL CP NH

n Some δCP regions excluded at 90%CL

Best-fit δCP/π 19 T2K future prospects

νe appearance prob. An-νe appearance prob. as large as ±25% (from δ=0)

sinδ=0 rejecon sensivity n Comparison btw ν and an-ν modes ν : an-ν = 1 : 1 enhances the sensivity to δCP n Plan: 50% ν + 50% an-ν modes True NH (unknown) à now running with an-ν mode

Main goals : n Exploring leptonic CPV (aiming for >3σ) n High precision νµ disapp. measurement n Important contribuon to MH determinaon 20 Other experiments : Many important results …

θ13 precision measurement by reactor experiments Double Chooz RENO Daya Bay What is this ?

and more … NOνA: Far detector me peak Borexino: pp solar ν IceCube: atm-ν osc.

21 (Leer of Intent) arXiv:1109.3262 (LBL study) arXiv:1412.4673 Hyper-Kamiokande hp://www.hyper-k.org/ Next generaon Mega-ton water Cherenkov detector

Total Mass : 0.99 Mton

Height Fiducial Mass : 0.56 Mton 54m ( x 25 of Super-K )

SK Aiming to start observaon in 2025 (3yrs for full survey & final designing + 7yrs for construcon) Wide physics program

n Proton decay search n Full picture of neutrino oscillaon (leptonic CP violaon, …) n Astrophysical neutrinos (solar ν, supernova ν, WIMP, …) n Neutrino geophysics Great potenal to discover new physics ! 22 5th open meeng in Vancouver Hyper-K project status (19-22 July 2014) n 6 open meengs held semiannually n 5 year grant for R&D and prototype detector from 2013 (Japan) n Selected as one of top 27 large-scale projects in “Master Plan 2014” of the Science Council of Japan n Funding requests in Canada, EU, Switzerland, and UK n Some already awarded n R&D in progress by HK internaonal WG n ~240 people from 13 countries n Hyper-K proto-collaboraon just formed n MoU between KEK-IPNS and ICRR n CDR to be prepared in a year

23 Summary n Super-K solar neutrino observaon n No clear signature of the spectrum “upturn” yet n 3σ day-night flux asymmetry à First direct indicaon of terrestrial maer effect n Super-K atmospheric neutrino observaon nd n Slightly favors normal hierarchy, 2 octant θ23 , and δCP~-π/2 n T2K oscillaon analysis

n Slightly favors NH and δCP~-π/2. 90%CL exclude regions on δCP

n Taking data with an-ν mode to enhance the sensivity to δCP n Hyper-K internaonal proto-collaboraon is formed n Baseline design exists. CDR to be prepared in a year. 24 Supplement

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