Neutrino Physics Double Beta Decay Junpei Shirai Research Center for Neutrino Science, Tohoku University PANIC, Sep.1, 2017, Beijing, China Neutrinoless 0νββ
Contents Introduction 0νββ and experimental challenges KamLAND-Zen Summary
Neutrinos : Finite Masses, but still mysterious ! ν Absolute val. of m ν s << m q,ℓ m ν Origin of the mass. problem ! Fundamental , ＞ 2 31 ν = ν ？ or ν = ν ? 2 32 τ θ , 12 θ 13 θ , 23 Δm , 21 2 Δm , e ν μ ν e μ τ δ CP Δm ＜ 0 ?
Dirac Mass term Majorana Mass term ν = ν ＜ 2 M N m ν Dirac Majorana ν N in the early Universe ! N: Important roles See-saw mechanism two mass eigenstates (M L /2)[(ψ c ) R ψ L +h.c.] + (M R /2)[(ψ c ) L ψ R +h.c.]. ν = ν − L m =M D (ψ R ψ L +h.c.) + ＝ M q,ℓ ＜ M q,ℓ
Matter dominance world (Leptogenesis) Sakharov’s conditions Super-heavy Majorana ν ΔL=0 =>Δ(B-L)=0 =>ΔB=0 Majorana nature of ν is very important and should be checked ! Big bang
Nuclear ββ decay provides the most feasible and sensitive way to study the Majorana nature of neutrinos !
n p There are ~35 natural isotopes , but very rare! W W β >2MeV Q β 124 Sn, 130 Te, 136 Xe, 150 Nd, etc. are observed 48 Ca, 76 Ge, 82 Se, 96 Zr, 100 Mo, 110 Pd, 116 Cd, SM process T 1/2 (A,Z+1) (A,Z+2) (A,Z) e (A,Z)→(A,Z+2)+2e - +2ν β β ν 2 e ν e e ν e which can double-beta decay. 0ν ～10 19 -10 21 yr n p X
Light Majorana νexch. is considered T 1 neutrino mass T 1/2 Not found =G (Q,Z)|M | 2 <m β β > 2 0 ν 0 ν / Effective 2 0 ν 1 <m β β > = | ΣU ei m i | 2 i =| (m 1 c 122 +m 2 s 122 e iα21 )c 132 +m 3 s 132 e i(α31-2δ) | All information of the neutrinos are contained; Oscillation parameters, Absolute ν masses, Majorana W as the dominant process. W 0 ν β β (A,Z)→(A,Z+2)+2e - A(Z) A(Z+2) A(Z+1) Beyond the SM process Total lepton number violation. Phase space factor Nuclear matrix element n p e e ν=ν m ν =0 Majorana CP-phases. 0ν ＞10 26 yr n p X
T 1/20ν lower limits (90%C.L.) and T 1/22ν NEMO-3 KamLAND-Zen GERDA CUORE AURORA NEMO-3 NEMO-3 ELEGANT-VI 19 NEMO-3 Log 10 T 1/20ν (yr) There are many ongoing and planned experiments ! Most sensitive experiments have provided T 1/20ν > 10^25~10^26 yr. T 1/20ν T 1/22ν 18 20 48 Ca 136 Xe 76 Ge 82 Se 96 Zr 100 Mo 116 Cd 150 Nd 130 Te 21 27 26 25 24 23 22 EXO-200
<m β <m β Normal mass hierarchy Inverted mass hierarchy K.K.( 76 Ge,1σ) Quasi- Degenerated mass hierarchy GERDA, CUORE, NEMO3,... KamLAND-Zen β > (eV) β > limit is close to the bottom of the QD region. <m lightetst > (eV) 10 -4 10 -3 10 -2 10 -1 10 -3 10 -2 10 -1 1 <m β β > <(61-165)meV Allowed region and upper limits on <m β β > QD Positive claim on 76 Ge was refuted (KL-Zen and GERDA). Ca Zr Nd Te Se Cd Te 1 Mo Ge Xe 136 − 1 (eV) 10 KamLAND-Zen ( Xe) IH m − 2 10 NH − 3 10 − − 3 − − 4 2 1 10 10 10 10 50 100 150 m (eV) A lightest
FOM for the sensitivity 2ν Region of interest (keV -1 kg -1 yr -1 ) Background index enrichment factor Isotopic abundance/ efficiency detection period Data taking Isotope mass Good energy resolution Remove BG (Ext./Int.) Large amount of isotope 0ν 2ν Current 10 25 ~10 26 yr √ Planned ~10 27 yr O(100)kg => O(1) ton T 1/20ν ∝εa MT bΔ E Isotope selection by large a, 0ν Q β β and long T 1/22ν Summed energy of electrons normalized by Q β β <m ββ >～0.02eV (IH) ～Energy resolution
Concept of the experiment Deep Underground Target nuclei Scalability Large amount Radio-purity Sensors Thick active shield Thick shield
Detection Strategy Event α/γ Internal external (U/Th) Rn γ n BG Scalability Efficiency ΔE Tracking PID topology Pulse shape e - Position Time TPC(Gas, Liq.) (A,Z)+LS Crystal Calorimetry Scintillation Phonons Ionization Signal E VTX PID e - (Bolometer)
Detection Strategy Internal KL-Zen CUORE Majorana BG n γ Rn (U/Th) external α/γ PANDAX-III ΔE Efficiency Scalability SNO+ 136 Xe 76 Ge 130 Te 130 Te 100 Mo SuperNEMO EXO, NEXT, e - Crystal e - PID VTX E Signal Ionization Phonons Scintillation Energy (A,Z)+LS AMoRE TPC(Gas, Liq.) Time Position Pulse shape Event pattern PID Tracking (Bolometry) GERDA 82 Se, 150 Nd
0 CUPID ( 82 Se) （ 76 Ge, SURF） MAJORANA （ 136 Xe, WIPP） EXO-200 ( 130 Te, SNOLAB) SNO+ （ 136 Xe, CanFranc） NEXT Modane） （ 82 Se, 150 Nd, 48 Ca, SuperNEMO LNGS (Italy) COBRA ( 116 Cd) CUORE（ 130 Te） ν GERDA（ 76 Ge） （ 136 Xe, CJPL） PANDAX-III MTD（ 150 Nd, KEK） AXEL（ 136 Xe, Kyoto） （ 48 Ca, Kamioka） CANDLES （ 136 Xe, Kamioka） KamLAND-Zen ( 100 Mo, Y2L） AMoRE activities in the world β β (Calorimetric, tracking/TPC)
GERDA* Prospects LAr Veto, PSD Analysis SiPMs PMTs PMTs 200kg Ge (Current Cryostat) 1000kg Ge T 0ν1/2 >10^27 yr (5yrs) T 0ν1/2 >10^28 yr (LEGEND) ΔE FWHM = detectors 2.8keV @Q(BEGe) Achieved ! μ-on veto ( 42 K) (SS vs MS, A/E) <m β β > ＜(10-20)meV Phase I Phase II enriched coaxial 35.6kg 37 HPGe GERmanium Detector Array T 0ν1/2 >5.3×10^25 yr (90%C.L.) LNGS 3600m.w.e. 76Ge Q: 2,039 keV enrich. HPGe Phase I+II 34.4kg yr BI=0.7 +1.1-0.5 ×10 -3 kg -1 keV -1 yr -1 <m β 7 Strings of β > ＜(150-330)meV Sensitivity T 0ν1/2 =4×10^25 yr No signal in ROI, BG free search ! 590m 3 water tank (10mΦ) + 66 PMT Ch. veto 64m 3 Liq.Ar cryostat (90 o K, 4mΦ) WLS Fiber curtain Phase II enriched BEGe
CUORE* β β > < (210-590)meV <m β > 6.6×10 24 yr CUORE Combined 38.1kg yr (10.6kg 130 Te) (5 yr) > 9×10 25 yr ΔE/E~0.2% @Q β Long-term stable operation of a ton-sized bolometric detector ! ×13piles) (4 crystals 1 tower Combined CUORE-0 (FWHM)@2615keV ΔE=7.9±0.6keV Challenging items Validation of the background model in ROI (α, β/γ) will be established. Jan.2017~: Cool down Heat sink 10mK radiation Incident holder Copper (Thermometer) NTD Ge sensor coupling 0.01 kg -1 keV -1 yr -1 thermal Weak (TeO 2 Absorber C∝T 3 ΔT∝E dep /C (FWHM) April-June: Science run (750kg) Cryogenic Underground CUORICINO Observatory for Rare Events CUPID CUORE Upgrade with Particle ID LNGS 3600m.w.e. 130Te Q: 2,528 keV Nat.TeO 2 34.1%( 130 Te) 988 TeO 2 65cm CUORE-0 > 2.8×10 24 yr ( 130 Te) 19.75kg yr (2003-2008) 9.8kg yr T 0ν1/2 ( 130 Te) CUORE > 4×10 24 yr 206kg( 130 Te) 19 towers CUORE est (ROI) MiDBD Heat Sink Copper Holder Weak Thermal Coupling NTD Ge Sensor Absorber (Thermometer) Crystal (TeO 2 ) Incident Radiation
136 Xe ν EXO, NEXT, TPC (Liq/Gas) light for Scintillation Zen KamLAND- bility to LS High solu- Scalability Excellent well established Techniques are life ! longest 2 Q β One of the High level of safety Non-flammable Non-toxic Chemical stability Purification Enrichment Rare gas β search！ β 136 Xe has nice characteristics for 0ν Nat. ab.=8.9% T 1/22ν =2.2×10 21 yr β =2.458MeV PANDAX-III
• • • • • • • • • • • σ/E=1.23% SS vs. MS <m Scintillation+Ionization Water 14m 13m planned installation at SNOLAB 5ton enriched Liq.Xe TPC nEXO Hardware upgrade (90%C.L.) β >＜(147-398) meV β (1.5±0.2)×10 -3 T 1/20ν > 1.8×10 25 yr 122 kg yr 44cm EXO-200 Enriched Xenon Observatory WIPP (NM,USA) 1585 m.w.e. 136Xe Q: 2,458 keV Liq.Xe TPC enrich:80.6% kg -1 keV -1 yr -1 Phase I (Sep.2011-Feb.2014) 40cm • Sensitivity: T 1/20ν ~ 10 28 yr (with Ba-tag) Phase II (Jan.-May, 2016) 55.6kg yr
NEXT* with a Xenon TPC NEXT-ton 83 Kr 5.5%@41.5keV => 0.7%@Q β CanFranc Neutrino Experiment Detector concept 0νββ search Electro- luminescence (S2) TPB coated surfaces Ionization Scintillation(S1) Tracking Plane (SiPMTs) for T 1/2 5×10^25 yr. β 100kg enriched Xe, NEXT-100 (2019~) 850 m.w.e. 136Xe Q: 2,458 keV 10-20bar TPC Electro-luminescence (EL) amplification ΔE/E~0.5% (FWHM)@Q β Energy Plane (PMTs) 1792 SiPMs, 12PMTs 50cm drift, 20cm radius, 5~10kg Xe, NEW (2015-2018) BG suppression. β Topological signature for TPB coated surfaces xenon TRACKING PLANE (SiPMs) ENERGY PLANE (PMTs) gas e - e - e - e - scintillation (S1) e - e - ionization electroluminescence (S2) CATHODE ANODE Full active volume rch
25-150μm 65m => 1% (Direct pixel readout without gas amplification) Cathode (100kV) 1.5m OFHC copper T 1/20ν ~10 27 yr 14m Water pool construction ΔE/E~3%(FWHM) @Q β finished in Jun.2016. World’s deepest ! 0.2μ’s/m 2 /d Horizontal shaft ! 2m Anode readout (MM) Prototype (16kg Xe, 10 bar) Micromegas with Microbulk Micromegas β . R&Ds for Readout; improve Q: 2,458 keV Mesh Pixel/strips PANDAX-III* Particle and Astrophysical Xenon Detector +TMA(1%), 3.5m 3 6720 m.w.e. 136Xe CJPL 90% enrich. TPC 200kg×5 200kg×5 Xe TPC modules in a water pool, ΔE/E~1%(FWHM) @Q β β . High press. (10bar) enriched 136Xe (200kg) • • • • • • • • • 6
KamLAND-Zen Ze ro- n eutrino double beta decay
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