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CANDLES for the study of 48 Ca double beta decay

CANDLES for the study of 48 Ca double beta decay. T. Kishimoto RCNP & Physics Dept. Osaka Univ. Contents. Double beta decay and Majorana Mass Matter dominated universe Neutrino mass Majorana neutrino and double beta decay Double beta decay of 48 Ca CANDLES detector Concept

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CANDLES for the study of 48 Ca double beta decay

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  1. CANDLES for the study of 48Ca double beta decay T. Kishimoto RCNP & Physics Dept. Osaka Univ.

  2. Contents • Double beta decay and Majorana Mass • Matter dominated universe • Neutrino mass • Majorana neutrino and double beta decay • Double beta decay of 48Ca • CANDLES detector • Concept • CANDLES I, II, III, VI, V • Prospect

  3. Baryon density in our Universe • Big bang nucleosynthesis • 4He, D, 3He, 7Li • Baryon density rB ~ 10－10 rg If particle number is conserved, Particle：1,000,000,001 Anti-particle：1,000,000,000 Matter dominated Univ. →CP + particle # →Double Deta decay

  4. Relativity + uncertainty →anti-particle ・no information is faster than light ・interact with any space-time →particle that travels backward in time →anti-particle Carries inverse quantity (charge spin(chirality)) time future light present distance Dirac equation →anti-particle past Charge: conserved Chirality: violated by mass

  5. Neutrino type • type Dirac Weyl Majorana • components 4 2 2 x 2 • yL yR mLmR Direction of propagation particle noscillation Dmn ~55 meV ~7 meV m=0 m≠0 Anti- particle Lepton number Chirality C, P CP

  6. Direct measurement of mn KATRIN => mn~ 0.2 eV • 3H b– decay (Qb: 18.7keV) • 0n decay • CMBR • WMAP + SDSS + … mn < ~ 0.6 eV

  7. 0n2b decay Possible in Standard model Majorana particle particle⇔anti-particle ・possible only for n ・matter dominated universe Sum energy spectrum 0n mode T >1025 yr 2n mode T ~1019 yr Effective mass Phase volume Nuclear matrix element

  8. n has to be a Majorana particle • Mass term (Dirac) • Mass term (Majorana) • Only Left (right) handed mass term can be made • Left and right can have different mass • We know only left-handed neutrino • Heavy right-handed n（see-saw mechanism） • Violates lepton number Chirality flip （relativity） Left handed → right handed (anti-particle) Leptogenesis

  9. Leptogenesis Fukugita, Yanagida (1986) • GUT ? (No proton decay?) SK • Majorana particle（Lepton number） • particle  anti-particle • CP • Anti-lepton＞Lepton(~10-10) • Instanton effect (t’Hooft) • Standard model • Anti-lepton → baryon • conserved： B-L Effective in early universe positron proton Proton decay(B-Lcons.) is irrelevant to the Baryogenesis : Yanagida

  10. Double beta decay nuclei AZ+1N-1 • Nuclei • 48Ca, 76Ge, 82Se,100Mo, • 128Te, 130Te, 136Xe, 150Nd • Positron emitter • Ultra rare process • 1020~25 yr • Huge natural background sources • High sensitive detector • Low background circumstance⇔Underground lab. AZN AZ+2N-2

  11. World Experiments

  12. Why 48Ca • Highest Q value (4.27 MeV, 150Nd: 3.3 MeV) • Large phase space factor • Little BG（g: 2.6 MeV, b: 3.3 MeV） • Natural abundance → 0.187% • Isotope separation →expensive(no Gas) • ~10g x 2 (in the world. only Early studies) • Next generation • Mn ~ T-1/2 ~ M-2(no BG) ~ M-4（BG limited） • 48Ca (no BG so far) • If we want to sense normal hierarchy region, only 48Ca + enrichment has a chance.

  13. Nuclear matrix element 2nbb decay e q1~0 n n1 p1 q2~0 n p1 n1 F2N(q=0) F2N(q) e q2 + q1~0 0nbb decay q2 - q1~pF e n1 p1 n p1 n1 Neutrino potential 1/r~A-1/3 e 2 nucleon correlation

  14. Matrix element 48Ca M0n f5/2 f7/2 forbidden if only f7/2(wf) And GT(op) p n M. Horoi (2010) wf: Configuration mixing Op: Higher partial wave ・ |M0n|2 ~5 ambiguity (accept and challenge) M(48Ca) is well estimated but not perfect yet. It is small though taken to be the minimum. A=48

  15. Oto Cosmo Observatory A tunnel constructed for a railroad but never used. It is 60km south from Osaka NPA 730　’04, 215 ELEGANT VI

  16. 48Ca double beta decay byELEGANT VI NPA 730　’04, 215 PRC78 058501(‘08) 1.76 y Qbb of 48Ca CaF2(pure) CaF2(Eu) CaF2(pure) CaF2(Eu) n = 1.44 CaF2(pure) n = 1.47 PMT PMT Not limited by backgrounds Silicon oil n = 1.40 Optical grease n = 1.47 But only 6.4g of 48Ca

  17. How to sense mn=1~10-2eV • Big detector • Huge amount of materials • Low radioactive background • Active shield • Passive shield • Low background material • BG rejection by signal processing • High resolution • Backgrounds from 2nbb decay • CANDLES is our solution

  18. CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer • CaF2(Pure) • 200kg, 300kg, 3t, • enrichment • 48Ca (Qbb=4.27MeV) • Liquid Scintillator • Wave Length Shifter • 4 p Active Shield • Passive shield • Photomultiplier • energy resolution Liquid Scintillator (Veto Counter) CaF2(Pure) Buffer Oil Large PMT

  19. CANDLES IBackground rejection POP(Proof of Principle) ADC(fast) ADC(total) liq. scint. : mineral oil + DPO (3 g/l) + Bis-MSB (0.3 g/l) Liquid Scintillator Liquid Scintillator CaF2 CaF2 ADC(total)

  20. Rejection of Double Pulse Sum energy ~ Q value Qa= 7.83MeV Qb = 3.27MeV b 212Po T1/2 = 0.299msec 208Pb a 212Bi 64% Qb = 2.25MeV Qa = 8.95MeV Typical Pulse Shape(100MHz FADC) 900ns 50ns Delayed Prompt • Reduction • 100MHz FADCDT >30ns(3ch) ; ~3% • 500MHz FADC (under preparation) . . . DT> 5ns ; ~1%

  21. Pulse Shape Discrimination Difference in decay time between a and g rays • PSD (Event by Event) • FADC (100MHz) • Afast/Aslow (Fast and slow component) • Discrimination between a and g(b) Events • Background Reduction ~ 0.3%

  22. Development of Low Background CaF2 Crystals • CaF2(Eu) in ELEGANT VI • U-chain(214Bi) : 1100mBq/kg • Th-chain(220Rn) : 98mBq/kg • Where is the crystals contaminated? CaF2 Powder Fused CaF2 CaF2 Crystal Raw Materials CaCO3, HF Radioactivities in CaF2 Powder (HPGe measurement) Radioactivities in CaF2(pure) Crystal (a-ray measurement) Powder selection Crystal making • U-chain(214Bi) ~41mBq/kg . . . 1/25 of Previous Crystals • Th-chain(220Rn) ~21mBq/kg. . . 1/5 of Previous Crystals

  23. Radioactive impurities CANDLES III(U.G.) CANDLES IV 3t 600k 300k

  24. CaF2(Pure) Energy resolution and BG rejection (2phase system) Visible light UV • BG from 2nbb • Energy resolution • CaF2：UV • PMT • 2 phase system Conversion phase Veto phase (absorves UV) 137Cs (662keV) 9.14% (FWHM) CaF2(pure) Counts (WLS phase) CANDLES I Liquid Scintillator Energy (keV)

  25. Liquid Scintillator CaF2(Pure) 10cm cube 15”PMT Mount System H2O CANDLES-II 45cm • Prototype S.Umehara Index 1.44@586nm (CaF2) Index 1.46@586nm (Mineral Oil) Cosmic-ray Events (High Energy)

  26. CANDLES III@Osaka PMT: 13”×32 15”×8 Observation at sea level Underground OK CaF2:191 kg 103cm3×60 Tank: Φ2.8×h2.6 m Rejection of external BG

  27. Kamioka Experimental hall D CANDLES III(UG) 3m f×4m h CANDLES III（UG） Kamioka KamLAND Lab D Super Kamiokande 4m 3m CANDLES CANDLES III(UG)

  28. CANDLES III（UG） CANDLES III（UG） 62 PMT’s 96 CaF2(pure) crystals (CaF2 crystals) Almost completed

  29. Mile stone • ELEGANTS VI • Best 48Ca 0nbb limit • CANDLES I, II • CANDLES III+ III(UG) • 100 x10cm3 CaF2 (~30 Bq/kg) ~0.5 eV • Start running in this October. • CANDLES IV • 3t CaF2 (3.5 kg 48Ca) (~3 Bq/kg) ~0.1 eV • CANDLES V • Enrichment and 0.3~1t of 48Ca (mn≦10meV) achieved

  30. Characteristic of CANDLES + Ba tagging Achieve both simultaneously • BG rate (events/weight) • So far the best • 2~3 orders • Scale up: • CANDLES IV, V • Enrichment • more bb nuclei • BGreduction

  31. - - - - Ca2+ - - Enrichment of 48Ca 48Ca：0.2% => 5~10 % C C O O C Dicyclohexano 18-crown-6 C O O DC18C6 C C O O C C • Increasebbnuclei • BGreduction • Crown ether • Sep. coeff.ε~ (3.5±0.5)x10-3 • Crown ether resin

  32. Enrichment for long migration ~7 hours 1m ~70hours 20m ~250hours 200m maximum: 0.0026 (original:0.0019) P r e l i m i n a r y Enrichment due to crown ether ・long migration length ・higher enrichment and larger amount ~7時間(1m) → ~250時間 (200m) amount: ×17, enrichment: ×8

  33. Ca ions in CE • Why CE absorbs 40Ca more than 48Ca? • CE: Harmonic oscillator pot. • Heavier Ca is in a lower energy state. • Water: （pH: 10-14 mol/ℓ） • H2O: polar molecule: HO pot. • Partition function ⇔ distribution • Mass dependence DE water CE meV~1% effect

  34. Other enrichment methods • Laser ionization • Plant for Uranium enrichment • KAERI 1kUS$/g (~1/100 of current CM value) • Centrifuge: high (0.6 MG) (JAERI) • Electrophoresis • Others • We will clarify the separation method in an year.

  35. Thank you.

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