Review of Neutrinoless Double Beta Decay

Maura Pavan: Neutrino Telescope 2025 1 Review of Neutrinoless Double Beta Decay Maura Pavan Università di Milano Bicocca e sez INFN di Milano Bicocca XXI Workshop on Neutrino Telescopes Padova September 29 – October 3 2025 Maura Pavan Università di Milano Bicocca e sez INFN di Milano Bicocca Maura Pavan Università di Milano Bicocca e sez INFN di Milano Bicocca Maura Pavan Università di Milano Bicocca e sez INFN di Milano Bicocca Maura Pavan: Neutrino Telescope 2025 2 Disclaimer In a 30-minute review you have to make choices, so here are mine. Some background + a selection (my personal one) of experiments. I apologize for not being able to properly report all the activities that are in progress in this field! Where possible, I’ll add timelines to show past progress and future goals, based on publicly available material — with future projections always linked to technical readiness. Any mistakes, inaccuracies, or omissions are entirely my responsibility and I apologize in advance for them. ●The CUPID 0 experiment – S. Fuνββ ●Latest results from the CUORE experiment P. Gorla ●LEGEND: 0 decay search with germanium detectors K. Gusevνββ ●Status of the SuperNEMO Experiment and physics objectives M. Petro ●The NEXT program and status of the NEXT-100 detector Brais P. Pazos Do not miss the talks we have at the conference Maura Pavan: Neutrino Telescope 2025 3 Neutrinoless Double Beta Decay 0nbb (A,Z)→(A,Z+2)+2e- ●violates Lepton Number DL=2 ●signature used for its identification is the sum E of electrons = Qbb Maura Pavan: Neutrino Telescope 2025 4 Neutrinoless Double Beta Decay 0nbb (A,Z)→(A,Z+2)+2e - +2 n e ●SM allowed ●rare but oserved Maura Pavan: Neutrino Telescope 2025 5 Why ? a window on BSM Physics oscillations L→flavor violated neutrinos have mass two options: → → ●Dirac massive neutrino (need to postulate L conservation) ●Majorana massive neutrino →D(B-L)=2 “natural” solution that may lead to a theory able to explain Problem of flavour Matter vs anti-Matter explain the observed fermionic mass spectrum and mixing Maura Pavan: Neutrino Telescope 2025 6 What do we measure with 0nbb? 1 T1/2 0 n =G0 n ⋅gA 4⋅M0 n 2⋅m bb 2 me 2 m bb =∑Uek 2mi Neutrino Majorana mass exchange of a light Majorana neutrino is the “reference” diagram (most “natural”) Majorana mass → mbb Maura Pavan: Neutrino Telescope 2025 7 What do we measure with 0nbb? 1 T1/2 0 n =G0 n ⋅gA 4⋅M0 n 2⋅m bb 2 me 2 +... m bb =∑Uek 2mi Neutrino Majorana mass other diagrams are possible depending on how the SM is extended →the decay rate is a sum over different contributions exchange of a light Majorana neutrino is the “reference” diagram (most “natural”) Majorana mass → mbb + …. Maura Pavan: Neutrino Telescope 2025 8 1 T1/2 0 n =G0 n ⋅gA 4⋅M0 n 2⋅m bb 2 me 2 Nuclear Physics Phase Space ●calculated ●increases with Qbb (motivation for the study of isotopes with large Qbb) PRC 85, 034316 (2012) Maura Pavan: Neutrino Telescope 2025 9 Nuclear Physics Nuclear Matrix Element ●calculation based on approximate solutions of the many-body nuclear problem ● RevModPhys 95, 025002 (2023) 1 T1/2 0 n =G0 n ⋅gA 4⋅M0 n 2⋅m bb 2 me 2 Maura Pavan: Neutrino Telescope 2025 16 Experiments ●Feasibility of enrichement ●Qbb (high Qbb large phase → space + low background) ●Energy resolution ●Active Background Rejection ●Scalability Isotope Tecnology Signature SUPRENEMO 82Se Qbb = 3 MeV NEXT 136Xe Qbb = 2.4 MeV Identification of daughter – Ba tagging (luminescence) s ROI ∼0.4 %→10 keV Maura Pavan: Neutrino Telescope 2025 17 Sensitivity requirements for future experiments ●Exclusion sensitivity = assume there is no signal, the 90% C.L. upper limit on halflife ●Discovery sensitivity = assume there is a signal, the 3s value for halflife Ingredients are: ●Mass (i.e. number of candidates) ●Time ●DE=ROI width FWHM energy resolution→ ●Background counting rate → counts/DE/M/T N.B. I will use ckky for B i.e. counts /(keV kg yr) Maura Pavan: Neutrino Telescope 2025 18 136Xe based 0nbb experiments: Two tecnologies adopted so-far: →diluted in liquid scintillator (KamLAND-ZEN) →single phase TPC liquid (EXO) or gas (NEXT) future: →dual-phase Xe TPC for DM searches will have large volumes PandaX-xT (43 ton) XLZ (60 ton) use huge amount of natural Xe → sizable 136Xe fraction → 136Xe diluted in LAr TCP (DUNE far detectors = 17 kton/module) Qbb = 2.4 MeV i.a. 8.87% gas, scintillator M. Schumann – XLZD DBD Summit May 2025 s ROI ∼0.65 %→15 keV Maura Pavan: Neutrino Telescope 2025 19 @ KAMIOKA ~2700 m.w.e VETO = Water Cherenkov DETECTOR = LS + PMT SOURCE = Inner Baloon = LS + enriched Xe (90% 136Xe) 6.7% √ E(MeV ) → s ROI ∼ 100 keV 13.7 cm √ E(MeV ) Energy Resolution Vertex Resolution Fiducial Volume and time-position cuts used to remove background - relevant cosmogenic contribution due to shallow depth. KZ-800 arXiv 2406.11438 KamLAND-ZEN Phased Experiment KZ-400 KZ-800 KZ-2→ → Maura Pavan: Neutrino Telescope 2025 20 ZEN-400 381 kg LXe purification ●100mAg removed New Inner Balloon ●more Xe ●better radioactivity KamLAND-ZEN ZEN-400 320 kg ZEN-800 745 kg 2010 2012 2014 2016 2018 2020 2022 2024 2028 2030 2032 2034 KZ-800 arXiv 2406.11438 ●Limited energy resolution full background → reconstruction needed to extract 0nbb KamLAND-ZEN 400+800 T1/2 0n > 3.8 x 1026 yr S1/2 0n = 2.6 x 1026 yr →mee < 28-122 meV Maura Pavan: Neutrino Telescope 2025 21 ZEN-400 381 kg KamLAND-ZEN ZEN-400 320 kg ZEN-800 745 kg 2010 2012 2014 2016 2018 2020 2022 2024 2028 2030 2032 2034 2 ZEN ~ 1 ton KamLAND2-Zen Goal S1/2 0n ~ 2 x 1027 yr in 5 yrs →mee < 12-53 meV KamLAND 2 ZEN – Major Upgrade Major Upgrade that aims at 5 times better sensitivity with similar isotope mass Main Factors Driving the new phase are ●improve energy resolution (new PMT+mirrors) sROI 4% to 2% ●reduce radioactivity (new OuterBalloon) ● improve background rejection (change LS in IB+ dead-time free electronics) Maura Pavan: Neutrino Telescope 2025 22 ●Ligth (175 nm) 4.5 m2 SiPM → ●Charge = segmented anode ●Bkg rejection using topology s ROI ∼1.2%→30 keV n-EXO @ SNOLab ~5890 m.w.e VETO = 1.5 kton Water Cherenkov - m tagging and shielding DETECTOR Liquid Xe single phase TPC SOURCE 5 tonne LXe enriched 90% 136Xe Maura Pavan: Neutrino Telescope 2025 23 nEXO EXO-200 200 kg enrXe 2010 2018 2034 2037 2045 EXO-200 @ WIPP ●BI ~ 2 x 10-3 ckky → S1/2 0n = 5 x 1025 yr ●T1/2 0n > 3.5 x 1025 yr m→ee < 93-286 meV Maura Pavan: Neutrino Telescope 2025 24 nEXO EXO-200 200 kg enrXe nEXO 5 ton natXe 2010 2018 2034 2037 2045 nEXO 5 ton enrXe NEXOv2.0 5 ton Goal S1/2 0n ~ 1 x 1028 yr - 10 yrs m→ee < 5-23 meV T. Brunner DBD Summit Heilderberg 2025 Maura Pavan: Neutrino Telescope 2025 25 CUORE @ LNGS (~3800 m.w.e) : ●988 TeO2 bolometers in operation since 2017 ●742 (206) kg TeO2 (130Te) ●High Energy Resolution ●No active bkg rejection 130Te based 0nbb experiments: High isotopic abundance, natural Te is already a good source →Te use pioneered with Low Temperature Calorimeters (Bolometers) s ROI ∼0.1 %→2 keV Qbb = 2.5 MeV i.a. 34% CUORE - 2 ton yr BI ~ 1.4 x 10-2 ckky S→1/2 0n = 4.4 x 1025 y T1/2 0n > 3.5 x 1025 yr m→ee < 70-250 meV A. Campani TAUP 2025 See S. Fu’s talk Maura Pavan: Neutrino Telescope 2025 32 ●High Qbb large phase space, lower background → ●Scintillating bolometer technnology e.g. using Li2MoO4 crystals ●Excellent Radiopurity ●High Energy resolution ●Alpha Background Rejection with Light/Heat 100Mo based 0nbb experiments: Qbb = 3.0 MeV i.a. 9.82% T1/2 2n ~ 7.1 x 1018 yr CUPID and AMORE different solution for the signal read-out CUPID = Ge thermistor as in CUORE AMORE = MMC (better performances reproducibility and read-out more challenging) Maura Pavan: Neutrino Telescope 2025 33 CUPID CUORE Upgrade with Particle IDentificaiton @ LNGS (~3800 m.w.e) Reuse CUORE infrastructure (cryostat & shields) ●upgrade of cryogenic system ●add m veto (plastic scintillators) DETECTOR 1596 Li2MoO4 scintillating bolometers → 240 kg 100Mo >95% ●Heat signal ●Light signal alpha rejection s ROI ∼0.07 %→2 keV Maura Pavan: Neutrino Telescope 2025 34 CUPID stage II: CUPID stage I CUPID 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 CUPID stage I: 80 kg 100Mo CUPID full experiment 240 kg 100Mo CUPID goal - 450 kg x yr BI ~ 1 x 10-4 ckky S1/2 0n ~ 1 x 1027 m→ee < 12-21 meV CUORE Precursors: CUPID-0 & CUPID-Mo ●scintillating bolometer technology CUORE ●operation of large bolometric arrays ●infrastructure BI in 100Mo ROI ~ 10-4 ckky (removing m & a) Maura Pavan: Neutrino Telescope 2025 35 AMORE 2020 2023 2028 2026 2030 2031 2032 2033 2034 2035 2036 AMORE-I AMORE-II stage I ~15 kg 100Mo AMORE-II stage I ~85 kg 100Mo AMORE II - 4 kg ( 00Mo) yr BI = 2.5 x 10-2 ckky T1/2 0n > 2.9 x 1024 m→ee <210-610 meV @Yemilab (700 m ) @Yemilab (~2500 m.w.e) AMORE II - 85 kg ( 00Mo) yr BI ~ 10-4 ckky T1/2 0n > 4 x 1026 m→ee <210-610 meV ●100Mo > 95% scintillating bolometers ●MMC read-out Maura Pavan: Neutrino Telescope 2025 36 CONCLUSIONS: mbb [meV] results in 2030-2033 100Mo CUPID stage I Maura Pavan: Neutrino Telescope 2025 37 CONCLUSIONS: mbb [meV] results in ~2040 100Mo CUPID mbb [meV]