Mo-enriched Li 2 MoO 4 scintillating bolometers for 0ν2β decay search: from LUMINEU to CUPID-0/Mo projects

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1 Mo-enriched Li 2 MoO 4 scintillating bolometers for 0ν2β decay search: from LUMINEU to CUPID-0/Mo projects D.V. Poda on behalf of the LUMINEU Collaboration CSNSM, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France Institute for Nuclear Research, MSP Kyiv, Ukraine in cooperation with LUCIFER MEDEX 17 meeting, Prague, 01 June 2017

2 LUMINEU and its follow up (CUPID-0/Mo) Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature Initially involved institutions: CSNSM and IAS Orsay, ICMCB Bordeaux, CEA Saclay (France); INR Kyiv (Ukraine); NIIC Novosibirsk (Russia); KIP Heidelberg (Germany); INFN Milano Bicocca (Italy) Further involved participants: EDELWEISS collaboration (France, Germany, UK, Russia); ITEP Moscow (Russia); INFN / LUCIFER coll. LNGS/Rome (Italy) New participants: LAL Orsay (France); Fudan Shanghai, USTC Hefei (China); MIT Massachusetts, UCLA California, UCB and LBNL Berkley (USA) R&D of the technology based on Mo-containing scintillating bolometers for a next-generation 0ν2β experiment Development of ZnMoO 4 / Li 2 MoO 4 based scintillating bolometers A pilot 0ν2β experiment with up to ~1 kg of Mo: LUMINEU project Extension to ~5 kg of Mo: CUPID-0/Mo project to prove the technology in view of CUPID (CUORE follow-up) 2

3 Advantages High Q ββ -value of Mo (3034 kev) T 1/2 (0ν2β) ~ Q 5 ; dominant γ bkg < 2615 kev ~10% of Mo in natural Mo Industrial Mo enrichment (> 95%) Reasonable cost ~80 $/g Variety of Mo-containing scintillators Active-source technique (~% efficiency) Some Mo based materials successfully tested as scintillating bolometer ZnMoO 4 initial choice by LUMINEU (2012) Li 2 MoO 4 parallel R&D by LUMINEU (2014) Warnings The choice of Mo-containing scintillator o Fastest 2ν2β process ( yr) Pile-up issue for slow response detectors o Weak γ line of 214 Bi close to Mo Q ββ 3054 kev, 0.021% B.R.; 2818 kev Compton edge o Weak hygroscopicity of Li 2 MoO 4 o 40 K issue for Li 2 MoO 4 (K is a homolog of Li) o Low light yield of Li 2 MoO 4 (~x0.5 of ZnMoO 4 at ~10 mk) RPP 80 (2017)

4 The choice of scintillating bolometer approach Scintillating bolometers Active-source technique High energy resolution Particle identification CUPID R&D arxiv: arxiv: ΔT = E C ΔV LUMINEU ~1 kev/mev ~0.1 mk/mev ~3 MeV ~ mv/mev LUMINEU demands in view of CUPID Sensor technology NTD Enriched isotope 90% Low material losses few % Radiopure crystal High performance 228 Th, 226 Ra 10 µbq/kg 10 kev ROI Rejection of α s 99.9% 4

5 LUMINEU R&D of Mo-enriched Li 2 MoO 4 crystals LUMINEU protocol of LMO production Mo-enriched molybdenum 1 kg ( Mo~99%; KINR) + 10 kg ( Mo~97%; ITEP) Deep purification of enriched material sublimation in vacuum recrystallization from aqueous solutions Advanced crystallization technology low-thermal-gradient Czochralski crystal growth possible size: 6 cm; 14 cm length of cylindrical part Dedicated R&D to control 40 K content in LMO selection of ultra-pure Li 2 CO 3 powder LMO growth by double crystallization R&D of Li 2 CO 3 purification is in progress Extraction of MoO 3 from residues arxiv: (Submitted to EPJC) Submitted to Cryst. Eng. Comm. Li 2 MoO 4 ~ kg 2015 Li 2 MoO 4 ~ 0.6 kg 2016 Li 2 MoO 4 ~ 0.8 kg Developed large mass Mo-enriched LMO high optical quality and scintillation properties high crystal yield (~ 80-85%) low irrecoverable losses of Mo (~3%) Ready for a batch production of Li 2 MoO 4 crystals

6 Li 2 MoO 4 crystals for low temperature tests Full cycle of LMO growth in NIIC (Russia) Deeply purified MoO 3 powder Commercial MoO 3 with natural isotopic abundance Mo-enriched Molybdenum (97%) used in NEMO-3 Commercial Li 2 CO 3 powder Novosibirsk Rare Metal Plant (Russia), by default Alfa Aesar (USA), for LMO-3 only Solid state synthesis of Li 2 MoO 4 compound LTG Cz growth from Pt crucible in air atmosphere Cutting, extraction of MoO 3 from residues Scintillator Mo purification Boule Produced elements crystalli- Subl. Recryst. ID Size (mm) Mass (g) zation Li 2 MoO 4 Single Double Single LMO Single Double Double LMO Single Double Single LMO Li 2 MoO 4 Double Double Triple enrlmo-1t enrlmo-1b Double Double Double enrlmo-2t enrlmo-2b arxiv: ; Submitted to Cryst. Eng. Comm. Nuclide NRMP Activity (mbq/kg) Alfa Aesar Sigma- Aldrich 228 Ra (8) 228 Th (4) 13(4) 226 Ra (30) 53(6) 40 K (70) 6

7 Used underground cryogenic facilities CUPID LNGS (Italy) LSM (France) Corno Grande 2912 m Roma 3600m w.e. Teramo 4800m w.e. Suspended systems to reduce vibrations muon veto Polyethylene (PE) PE Pb Cu Pb See e.g. in arxiv: neutron counter 7

8 From single Li 2 MoO 4 module to x4 Li 2 MoO 4 array CUPID R&D EDELWEISS LMO-1 enrlmos ~3 years of LUMINEU activity 8

9 Tests of Li 2 MoO 4 -based scintillating bolometers Detector Crystal ID Crystal mass (g) Light detector standard Lab Temperature (mk) Acquired data (h) Li 2 MoO 4 LMO IAS LNGS LMO-2 LMO LUCIFER IAS LNGS Li 2 MoO 4 enrlmo-1b 204 LUCIFER LNGS enrlmo-1t 186 LUMINEU LSM enrlmo-1t enrlmo-1b enrlmo-2t enrlmo-2b LUMINEU LSM Ge light detector by Diameter (mm) Thickness (mm) Antireflecting coating NTD mass (mg) IAS No ~1 LUCIFER No 9 LUMINEU nm SiO 5-9 arxiv:

10 Performance & radiopurity of Li 2 MoO 4 bolometers LMO g LMO g LMO g Signal [nv/kev] FWHM 2615 kev 4 ± 1 6 ± 1 5 ± 1 LY γ(β) [kev/mev] * DP α/γ(β), > 2.5 MeV Discrimination Power between α and γ(β) arxiv: LMO-2, 232 Th (45 h), MeV data DP α/γ(β) = 9 α, 99.9% γ(β), 99.7% α, 5σ α % Activity (mbq/kg) α, 9σ α Powder NRMP LMO-1 Single cr. LMO-2 Double cr. Powder Alpha Aesar LMO-3 Single cr. 228 Th (4) Ra (30) 0.13(2) 40 K 42 62(2)

11 LUMINEU light detectors performance Light detectors coupled to Li 2 MoO 4 bolometers Light detector 1b-LD Conditions optimal over bias Signal µv/kev FWHM Bsl kev b-LD, 46 h 60 Co (~ 200 kbq) EDW regen runs 1t-LD optimal over bias b-LD optimal over bias t-LD optimal over bias LUMINEU 17 mk CUPID-0 20 mk Performance of CUPID-0 LDs: EPJC 76 (2016) 364 Effect of LD performance on α/γ DP: FWHM Bsl ~ 0.5 kev expected DP ~ 8 FWHM Bsl ~ 0.1 kev expected DP ~ 14 Good reproducibility of standard high performance 11

12 Performance of Li 2 MoO 4 bolometers enrlmo-# 1t 1b 2t 2b 20 mk 17 mk 17 mk 12 mk 17 mk 17 mk Signal [nv/kev] FWHM 0 kev FWHM 2615 kev ~1.2 ~1.0 ~1.2 ~1.2 ~2.4 ~ ± ± ± ± ± ±0.6 ~5-6 kev Q ββ Mo (3034 kev) Excellent performance 12

13 Neutron spectroscopy with Li 2 MoO 4 bolometers enrlmo-1t, AmBe (290 h) Li 2 MoO 4 7.6% of 6 Li 6 Li + n t + α (Q = 4783 kev) E(t+α) = 4783 kev (thermal n, ~25 mev) E(t+α) = 5022 kev ~240 kev) 6 Li(n,t)α thermal n FWHM = 7.9(1) kev 6 Li(n,tot) 98 Mo(n,tot) Mo(n,tot) 16 O(n,tot) 7 Li(n,tot) 6 Li(n,t)α, resonance Prospects for in-situ neutron detection Advantages ~% detection of thermal n clear α+t Q+E n γ(β) background-free ROI world record resolution of thermal n capture on 6 Li (6-11 kev 4783 kev) 13

14 Light-assisted particle identification for Li 2 MoO 4 enrlmo-# 1t 1b 2t 2b M3 reflecting foil yes no yes no yes yes LY γ(β) [kev/mev] n.a DP α/γ(β), > 2.5 MeV * * - Data selection for DP: γ(β) s in MeV, α s ~ 5.4 MeV 210 ae Po or ~ 4.8 MeV 6 ae Li(n,t)α enrlmo-2t, AmBe (290 h) With M3 foil enrlmo-1t, AmBe (290 h) No M3 foil DP α+t/γ(β) = 14 DP α+t/γ(β) = 9 Full α/γ(β) separation 14

15 Particle identification by heat channel LMO-1, AmBe (20 h), 2 ksps sampling rate DP=5.7 DP=8.2 arxiv: Ability to particle identification by only heat signals 15

16 First background measurements with Li 2 MoO 4 Scintillation of M3 reflecting foil enrlmo-1t, Bkg (1303 h), LSM α MeV ~0.1 cnts/(kev kg yr), similar to CUORICINO Scintillation of M3 reflecting foil enrlmo-1b, Bkg (319 h), LNGS Low Σ α rate High radiopurity of both enrlmos arxiv:

17 Background measurements with 4 Li 2 MoO 4 array Preliminary enrlmo-1t, 624 h enrlmo-2t, 666 h No bright α s enrlmo-1b, 587 h enrlmo-2b, 666 h No bright α s Surface 226 Ra High radiopurity of enrlmos + α s in MeV ~0.2 cnts/yr/kg/kev 17

18 α Background of Li 2 MoO 4 detectors enrlmo-1t 1303 h June 2016 enrlmo-1b 487 h June 2016 arxiv: arxiv: enrlmo-1t 905 h Feb enrlmo-1b 898 h Feb Surface 226 Ra Preliminary enrlmo-2t 943 h enrlmo-2b 666 h 18

19 α Background of Li 2 MoO 4 detectors enrlmo-1t 1303 h June (2) mbq/kg enrlmo-1b 487 h June (1) mbq/kg 6 Li(n,t)α, 4784 kev Thermal n flux in EDW n/cm 2 /sec Other U/Th 3-8 µbq/kg n flux in CUPID R&D n/cm 2 /sec Other U/Th 6-11 µbq/kg enrlmo-1t 905 h Feb (3) mbq/kg Preliminary enrlmo-1b 898 h Feb surface 0.04(1) mbq/kg 0.20(2) mbq/kg enrlmo-2t 943 h 0.08(1) mbq/kg enrlmo-2b 666 h 0.02(1) mbq/kg 19

20 γ(β) Background of Li 2 MoO 4 detectors enrlmo-1t Preliminary No muon veto clock No muon veto clock enrlmo-1t, 905 h Dominant γ(β) Bkg: 2ν2β Mo ~10 mbq/kg 40 K 1.3 mbq/kg muons, pile-ups? enrlmo-1b, 901 h enrlmo-2t, 943 h enrlmo-2b, 666 h muons, pile-ups? enrlmo-# 1t 1b 2t 2b Average Rate [cnts/day/kg] of 2615 kev γ s 1.5(4) 0.7(3) 2.1(5) 1.3(5) 1.0(3) 1.1(2) Position dependent γ(β) rate inside the EDELWEISS set-up 208 Tl rate is ~x40 of CUORICINO background Work is in progress to reduce the external 232 Th background 20

21 Sensitivity to 0ν2β decay of Mo Li 2 MoO 4, 0.11 kg yr No muon veto clock Preliminary Background in MeV: 0.06(3) c/yr/kg/kev Mo Q ββ (3034 kev) Sensitivity to Mo 0ν2β decay: Q ββ ( Mo) = 3034 kev ROI = 10 kev Q ββ eff 0ν2β = 73% in ROI eff PSD = 97% Enrichment = 96.9% of Mo Exposure = 39 kg d BI = 0.06 cnts/yr/kg/kev Bkg = counts in ROI Signal = 0 lims = 2.38 counts at 90% CL T 1/2 = % CL <m ββ > ev NEMO-3 (34.3 kg yr): T 1/ % CL PRD 92 (2015) High potential of scintillating bolometers approach 21

22 Investigation of 2ν2β decay of Mo Enriched LMO, 28.7 kg d Preliminary Signal / Bkg ~ 10 in MeV Measurement of Mo 2ν2β decay: Exposure = 29 kg d Enrichment = 96.9% of Mo eff PSD = 96.4% Fit in kev Effect = ± 229 decays T 1/2 = [6.92±0.06(stat)] yr Systematic error = 6.5% Crystals mass % Mo enrichment 0.2 % PSD cut efficiency 0.4 % Trigger efficiency 0.5 % Monte Carlo 5 % Fit 1.1 % One of the most precise Mo half-life value T 1/2 [10 18 yr] Exposure Experiment Ref. 7.11±0.02(stat)±0.54(syst) 7.37 kg yr NEMO-3 PRL 95, (2005) 7.15±0.37(stat)±0.66(syst) 0.08 kg yr LUCIFER JPG 41, (2014) 6.90±0.15(stat)±0.42(syst) 0.03 kg yr LUMINEU arxiv: ±0.06(stat)±0.36(syst) 0.08 kg yr LUMINEU MEDEX 17 22

23 LUMINEU follow-up: CUPID-0/Mo CUPID-0/Mo Phase I (20 crystals): 20 Mo-enriched (97%) Li 2 MoO 4 ( mm, 0.21 kg each; 4.18 kg total) 2.34 kg of Mo ( Mo nuclei) 20 Ge light detectors ( mm)+sio EDELWEISS LSM (France) CUPID-0/Mo Phase II (20+20 crystals): Additional 20 Li 2 MoO 4 CUPID-0 LNGS (Italy) or CROSS Canfranc (Spain) First 20 crystals have been delivered CUPID-0/Mo Phase I in EDELWEISS set-up 23

24 ROI = 10 kev window Efficiency = 69% ε 0ν2β = 73%, ε PSD = 95% BI = 10-3 cnts/yr/kg/kev Options (1) and (2) are substantially unchanged by BI = 10-2 cnts/yr/kg/kev (lower T 1/2 by 6%, 16%, 37%) CUPID-0/Mo sensitivity CUPID-0/Mo configuration T 1/2 sensitivity [yr] 90% CL <m ββ > [ev] (1) cr. yr (2) cr. yr (3) cr. yr CUPID-0/Mo sensitivity LUMINEU (0.06 kg yr Mo) (1) 1.2 kg yr Mo (2) 3.5 kg yr (3) 14 kg yr ββ Nuclide Exposure [kg yr] 130 Te 29.5 Mo Ge Xe 504 PRL 115 (2015) PRD 92 (2015) Nature 544 (2017) 5 PRL 117 (2016) RPP 80 (2017)

25 Summary Prospects of Li 2 MoO 4 scintillating bolometers for high-sensitivity 0ν2β searches have been unambiguously proved by results of LUMINEU project Developed mass production technology of high quality radiopure Li 2 MoO 4 Established technology of high performance Li 2 MoO 4 bolometers array Achieved reasonably high sensitivity to Mo 0ν2β decay of over a short exposure Performed one of the most precise measurements of the 2ν2β decay half-life of Mo LUMINEU is extended to CUPID-0/Mo 2β experiment as a demonstrator of the Li 2 MoO 4 scintillating bolometer technology for CUPID project ββ Source: ~5 kg of Mo embedded in 40 Li 2 MoO 4 crystals 0.2-kg each Start by: end of 2017 (20 crystals) and mid (20+20 crystals) Ambitious results in 3 yr: the best accurate Mo 2ν2β half-life value and one of the highest sensitivity to effective Majorana neutrino mass Main goal: demonstration of the LUMINEU technology viability for CUPID, next generation 1t-scale bolometric 0ν2β project (CUORE follow up) 25