New Results from the CUORE Experiment

CUORE

New results from the CUORE experiment

Irene Nutini 9th International Conference Università degli Studi Milano Bicocca on New Frontiers in Physics INFN Milano Bicocca (ICNFP 2020) September 8th, 2020 I.Nutini, ICNFP2020 conference - September 8th, 2020 1 Outlook

• Double beta decay • The CUORE experiment • CUORE physics data taking • New results from CUORE: • 0vββ decay search • 2vββ decay measurement and background • 0vββ/2vββ decay to excited states

I.Nutini, ICNFP2020 I.Nutini,conference GSSI - September 8th, 2020 2 Double beta decay CUORE Double beta decay is a rare nuclear decay: (N,Z) → (N-2, Z+2)

Two neutrino double Neutrinoless double beta decay (2vββ) beta decay (0vββ)

- 2nd order process - Beyond SM process allowed in SM (ΔL = 0) (ΔL = 2) - Observed in several - Not yet observed 1/2 24-26 nuclei: T1/22vββ ~ 1018-24 yr T 0vββ >10 yr

2vββ v 0vββ v

Q Q-value of the ββ decay

I.Nutini, ICNFP2020 conference - September 8th, 2020 3 The CUORE experiment CUORE CUORE: Cryogenic Underground Observatory for Rare Events

Cryogenic experiment: ~1 ton solid state calorimeter 988 (nat)TeO2 crystals operated at ~10 mK - large mass and high granularity -

Experiment located at Laboratori Nazionali del Gran Sasso (LNGS), Italy

CUORE

Primary goal: search for 0vββ decay of 130Te CUORE 0vββ projected sensitivity:

S0v ~ 9 x 1025 yr (90% C.L.) in 5 years

Artusa D.R. et al. (CUORE Collaboration), Adv. High Energy Phys. 2015,879871,(2015) mββ < 50-130 meV http://doi.org/10.1155/2015/879871

I.Nutini, ICNFP2020 conference - September 8th, 2020 4 TheThe CUORECUORE experimentchallenge Low background CUORE • Deep underground location (LNGS) Overburden: 1400 m calcareous rock (3600 m.w.e) Cosmic ray rate reduction: 10-6 relative to the surface • Strict radio-purity controls on materials and assembly • Passive shields (Pb) from external and cryostat radioactivity • Detector: high granularity and self-shielding Background goal: 10-2 c/(keV⋅kg⋅yr)

in the Region Of Interest (ROI) around Qββ Low temperature and low vibrations

TeO2 detectors to be operated as bolometers at temperature ~10 mK: need for cryogenic infrastructure • Multistage cryogen-free cryostat: Cooling systems: Pulse Tubes (PTs) and Dilution Unit (DU) - Mass to be cooled < 4K: ~ 15 tons (IVC volume and Cu vessels, Roman Pb shield) - Mass to be cooled < 50 mK: ~ 3 tons (Top Pb shield, Cu supports and TeO2 detectors) • Mechanical vibration isolation Reduce energy dissipation by vibrations Target energy resolution: 5 keV FWHM Dell'Oro S. et al., Cryogenics 102, 9, (2019) in the Region Of Interest (ROI) around Qββ https://doi.org/10.1016/j.cryogenics.2019.06.011 I.Nutini, ICNFP2020 conference - September 8th, 2020 5 Double beta decay with TeO2 bolometers CUORE

Beneﬁts of using (nat)TeO2 detectors:

• 130Te natural isotopic abundance η(130Te) = 34.167%, no 4500 48 need for further enrichment after the growth of natural Ca 4000

crystals 96 3500 Zr 150Nd Eα (Bi) 3.27 MeV 130 100 • Qββ ( Te) = 2527.518 keV, above most of the natural 82Se Mo 3000 116 Eγ (Tl) 2.615 MeV Cd 130 radioactivity 136Xe Te 2500 124Sn • 130 76Ge Te within the detector absorber of TeO2 (ε ~ 90%) 2000 Q-value [keV] • Reproducible growth of large number of high quality and 1500

high purity crystals; large active mass detector (crystals 1000 128Te ~ 1kg, ~1000 crystals) 0 5 10 15 20 25 30 35 • TeO2 operated as low temperature detectors (~10 mK): Isotopic Abundance [atomic %] very good energy resolution Δ (~0.1-0.2% FWHM/E at Qββ ), allows a better reconstruction of the background spectrum and a reduction of 2νββ decay irreducible background around Qββ

Artusa D.R. et al. (CUORE Collaboration), Adv. High Energy Phys. 2015,879871,(2015) http://doi.org/10.1155/2015/879871

I.Nutini, ICNFP2020 conference - September 8th, 2020 6 CUORE and the bolometric technique CUORE CUORE TeO2 detectors are operated as cryogenic bolometers sensitive to phonons Temperature sensor Heat bath Low heat capacity @ T ~ 10 mK Excellent energy resolution (~0.2% FWHM) AbsorberCrystal Same detector response for different particles (heat only) Slowness if coupled with NTDs (suitable only for rare event searches)

Energy −5000 Thermal coupling release −5500 Amplitude (a.u.) Amplitude

Simpliﬁed thermal model: −6000

One thermal capacity C (crystal) ∆ T −6500 One thermal link G (btw crystal/heat bath)

−7000 Edep 100µKG ⌧ T ⌧ = 1s / C ⇡ MeVC ⇡ −7500 02468 10 Amplitude of the pulse ∝ ΔT ∝ Energy deposition Time (s)

I.Nutini, ICNFP2020 conference - September 8th, 2020 7 TheThe CUORECUORE experimentdetector CUORE CUORE instrumented bolometers

Au-wire bonding to Cu-PEN read-out strips

PTFE holders

TeO2 absorber Ge-NTD thermistor Si-heater

CUORE detector

Array of closely packed 988 TeO2 crystals arranged in 19 towers High Mass of TeO2: 742 kg (206 kg of 130Te )

Alduino C. et al. (CUORE collaboration), J. Inst. 11(07), P07009, (2016) https://doi.org/10.1088/1748-0221/11/07/p07009

I.Nutini, ICNFP2020 conference - September 8th, 2020 8 CUORE data taking CUORE • Data taking started in Spring 2017 • After initial data taking phase, signiﬁcant effort devoted to understanding the system and optimizing data taking conditions • Since March 2019 data taking is continuing smoothly with > 90% uptime • CUORE “data set”: ~1 month of background data taking with a few days of calibration at the start and end

CUORE preliminary Reached 1 ton yr of raw exposure!

yr) 1000 280 CUORE Run Time Breakdown yr) ⋅ ⋅ Exposure accumulation - August 2020 260 Phys. Rev. Lett. 124, 122501 (2020) 240 70.5 % 800 220 Exposure (kg 200

180 Te Exposure (kg

600 130 160 1.6 % 2.1 % 140 5.4 % 120 400 100 14.0 % 80

200 60 Background Calibration 40 Down Time NPulses 20 Setup Test 0 0 Jul-2017 Dec-2017 Jul-2018 Dec-2018 Jul-2019 Jan-2020 Jul-2020

I.Nutini, ICNFP2020 conference - September 8th, 2020 9

6.4 % TheCUORE CUORE data experiment processing CUORE

−5000 Run: 302188 Channel: 42 IsSignal: 1 −5500

Voltage (mV) NumberOfPulses: 1 SingleTrigger: 1

−6000

−6500 Optimum Gain Energy Coincidences −7000 Filter Correction Calibration

−7500

0 2 4 6 8 10 Time (s)

2 1 10 Average Pulse 10 /Hz) Filtered Average Pulse 2 1 0.8 10−1 M1 10−2 0.6 −3

Amplitude (a. u.) 10

ANPS (mV 10−4 0.4 10−5 10−6 0.2 10−7 10−8 −9 0 10 Average Noise PS M2 10−10 −0.2 10−11 Filtered Average Noise PS 10−12 0 2 4 6 8 10−1 1 10 102 Time (s) Frequency (Hz) Matched ﬁlter that maximizes the signal-to-noise ratio 2000 Voltage (mV) 5050 1500 2915 5040 2910 5030 1000 2905 5020 Amplitude (mV) 5010 2900 StabAmplitude (a.u.) 500 5000 2895 4990 27 ms 2890 4980 0 4970 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 2885 Time (s) 4960 2880 4950 −5800 −5600 −5400 −5200 −5000 −5800 −5600 −5400 −5200 −5000 Baseline (mV) Baseline (mV) Heater pulses for thermal gain stabilization I.Nutini, ICNFP2020 conference - September 8th, 2020 10 TheNew CUORE results fromexperiment CUORE: 0νββ analysis CUORE Summed Spectrum

Total exposure for 0νββ decay search (PRL2020) CUORE 208Tl 372.5 kg yr natTeO , 130Te exposure: 103.6 kg yr 250 Exposure: 372.5 kg yr 2 Blinded (After analysis selections) 200 Unlinded Events [counts/keV]

150 Qββ - Blinding of the background spectrum: optimization of analysis procedures and 100

selections 50 214Bi 60Co - Event selection is performed after discarding 0 2400 2450 2500 2550 2600 2650 2700 periods of low quality data (about 1% of live time) Reconstructed Energy [keV] - Detector response function built on the 2615 keV calibration line. Apply a scaling factor to obtain Combined Calibration Fit (DS 2) 2 the correct energy resolution at Qββ :(7.0 ± 0.4) 1.5 1 Ratio 0.5 keV FWHM 0 2540 2560 2580 2600 2620 2640 2660 2680 2700 2720 - Containment efﬁciency for a 0νββ decay to be single site event (evaluated via MC) - (88.350 ± 104 0.090)% 3 - Selection efﬁciencies (evaluated on data): trigger, 10

energy reconstruction, pile-up rejection, Counts/ (2 keV) 102 multiplicity, PSA - (87.54 ± 0.17)%

10 2540 2560 2580 2600 2620 2640 2660 2680 2700 2720 Reconstructed Energy (keV)

16 90% limit on Γ0ν - Unblinded data: 14 - Bayesian Analysis (BAT) 12 - Likelihood model: ﬂat continuum (BI), posited 10 peak for 0νββ (rate), peak for 60Co (rate + 8 Qββ position) 6

- Unbinned ﬁt in ROI [2490,2575 keV] on Events [counts/1.0keV] 4 physical range (rates non-negative), uniform 2 prior on Γ0ν 0 - 2480 2500 2520 2540 2560 2580 Systematics: repeat ﬁts with nuisance Energy [keV] parameters, allow negative rates (<0.4%

impact on limit) 90% C.I. 0.6

No evidence of signal. 0.5 Posterior of Γ0ν: extract an upper limit on decay rate. 0.4 ] | Data) -1

[yr 0.3 ν 130 0 Half-life limit for 0vββ in Te Γ

P( 0.2 T0ν1/2 (130Te) > 3.2 × 1025 yr (90%C.I including syst.) 0.1

−24 0 ×10 −0.1 −0.05 0 0.05 0.1 [yr-1] Alduino C. et al. (CUORE collaboration), Phys. Rev. Lett. 122, Γ0ν 122501, (2020), https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.122501 I.Nutini, ICNFP2020 conference - September 8th, 2020 12 TheNew CUORE results fromexperiment CUORE: 0νββ analysis CUORE Repeating the ﬁt in the ROI, without the 0νββ decay contribution ROI background index (B) = (1.38 ± 0.07) × 10-2 c/(keV⋅kg⋅yr)

Exclusion sensitivity for 0νββ decay: Generate pseudo-experiments with bkg-only hypothesis, ﬁt the ROI with bkg+signal hypothesis

CUORE median exclusion sensitivity on 130Te halﬂife: T0ν1/2 (130Te) = 1.7 × 1025 yr Probability to get a more stringent limit given the current sensitivity: 3.2%.

3 3 10 10 CUORE Preliminary Mo Limit on 0νββ decay half life and Se interpretation in context of light Majorana Ge

2 CUORE limit (Te), PhysRevLett.124.122501 102 neutrino exchange: 10 Xe CUORE sensitivity (Te) mββ < 75 - 350 meV at 90% C.I. Inverted hierarchy

10 10 (meV) β β m

Normal hierarchy

1 1

Other isotopes −1 −1 10 10 10−1 1 10 1002 0.2 0.4 0.6 0.8 1 mlightest (meV)

Alduino C. et al. (CUORE collaboration), Phys. Rev. Lett. 122, 122501, (2020), https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.122501 I.Nutini, ICNFP2020 conference - September 8th, 2020 13 TheNew CUORE results fromexperiment CUORE: 2vββ decay CUORE Reconstruction of the CUORE continuum background: • GEANT4 simulation + measured detector response function to produce expected spectra • 61 background sources simulated, bayesian Modern Pb MCMC ﬁt with uniform priors (except muons) +++

+++ • Exploit coincidences & detector self-shielding toRoman Pb Detector constrain location of sources Towers Adams, D. Q. et al. (CUORE Total exposure for 2vββ analysis: 300.7 kg yr Collaboration),"Update on the recent progress of Roman Pb the CUORE experiment" arXiv:1808.10342, (2018)

Summed background spectrum Reconstructed Spectrum (Multiplicity 1) CUORE preliminary 4 CUORE Preliminary 10 210Po 60Co 40K 190Pt

103 208Tl 232Th/238U Events [counts/keV] Events

214Bi CUORE preliminary (300.7 kg yr) 102

2vββ-ROI 10

1 0 1000 2000 3000 4000 5000 6000 Reconstructed Energy [keV]

Systematic uncertainties: - Data selection: geometric splitting, time splitting, ﬁt range - Choice of 2νββ spectrum (SSD

CUORE preliminary (300.7 kg yr) vs HSD) - Unconstrained fallout products (90Sr)

“CUORE Results and the CUPID Project” at Neutrino 2020 conference, https://indico.fnal.gov/event/43209/contributions/187866/attachments/ Paper in preparation 129542/159294/CUORE_CUPID_Nu2020.pdf I.Nutini, ICNFP2020 conference - September 8th, 2020 15 TheNew CUORE results fromexperiment CUORE: excited states CUORE Search for 0νββ and 2νββ decays of 130Te to the ﬁrst 0+ excited state of 130Xe - Double beta decay can proceed also through transitions to the various excited states of the daughter nucleus - 2νββ decay to the 0+ excited state observed in 100Mo and 150Nd, with half lives of the order of few 1020 yr - Previous attempts of measuring the ββ decay of 130Te to the ﬁrst 0+ excited state of 130Xe made by both CUORICINO and CUORE-0: (T1/2)0ν0+ > 1.4 × 1024 yr (90% C.L.), (T1/2)2ν0+ > 2.5 × 1023 yr (90% C.L.)

Signature of the decay: Cascade of de-excitation γs in coincidence with βs - multi-site signatures - background reduction with respect to the corresponding transitions to the ground state, especially in case of a high detector granularity

γ (1257) M2 ββ M3 γ (1257) ββ γ (536)

γ (536)

I.Nutini, ICNFP2020 conference - September 8th, 2020 16 TheNew CUORE results fromexperiment CUORE: excited states CUORE Considering only fully contained events for the analysis Experimental signatures considered for the analysis: - 2A0-2B1: Multiplicity 2, crystal1= ββ + γ(536) & crystal2 = γ(1257) - 2A2-2B3: Multiplicity 2, crystal1= γ(536) & crystal2 = ββ + γ(1257) - 3A0: Multiplicity 3, crystal1= ββ & crystal2= γ(536) & crystal3 = γ(1257) These are the signatures which contribute the most to the discovery sensitivity in the ββ decay rate

0νββ, sig. 2A2-2B3 2νββ, sig. 2A2-2B3

CUORE preliminary CUORE preliminary No evidence of signal for both 0νββ and 2νββ decays of 130Te to 130Xe 0+ excited state

0vββ: (T1/2)0ν0+ > 5.9 × 1024 yr (90% C.I.) 2vββ: (T1/2)2ν0+ > 1.3 × 1024 yr (90% C.I.)

crystal1 ~ E in[523, 573], γ (536) crystal1 ~ E in[523, 573], γ (536) crystal2 ~ E in[1981, 2001], ββ (734) + γ (1257) crystal2 ~ E in[1360, 1990], ββ (0-734) + γ (1257)

CUORE is the ﬁrst tonne-scale operating bolometric 0νββ detector. • New CUORE physics results of 130Te 0νββ and 2νββ decays to ground and excited states with the physics data collected in 2017-2019 • A raw exposure of ~ 1 ton yr has been achieved and data-taking is proceeding, updated results for 1 ton yr total exposure (after analysis cuts) will be released soon! • The CUORE data taking is currently underway to collect 5 years of run time • Important feedback from CUORE operations for the future CUPID project (CUORE Upgrade with Particle IDentiﬁcation)

18 Thank you on behalf of The CUORE collaboration

CUORE

I.Nutini, Lomonosov conference - August 23rd, 2019 19 Backup

20 Neutrinoless double beta decay CUORE Observation of 0vββ decay would imply: - Lepton number violation - presence of a Majorana term for the neutrino mass - Constraints on neutrino mass hierarchy and scale

Majorana mass term 0vββ favorite mechanism: coupling Light Majorana neutrino the two neutrinos exchange

103

Current limits from 0vββ experiments

2 From 0vββ decay rate measurements one can infer 10 the effective neutrino mass term Inverted hierarchy

10 (meV) 10

1 β 2 2 β

G(Q ,Z) M m m T 0⌫ / | nucl| | | 1/2 Normal hierarchy

1 Phase space integral Nuclear matrix element (NME) Effective neutrino mass term 10−1 2 10−1 1 10 102 m (meV) m = ⌃ m U lightest | i ⌫i ei| 21 21 Neutrinoless double beta decay CUORE Experimental 0vββ half-life sensitivity From 0vββ decay rate measurements one can infer the effective neutrino mass term 2vββ Finite background M T v 0vββ Detector performance v S ⌘ ✏ · 0⌫ - vv / · · B extremely low r · background - excellent energy Background free resolution (B · Δ << 1) Detection technology 103 - Good detection efﬁciency: S ⌘ ✏ M T 0⌫ / · · · ββ source embedded into Current limits from 0vββ experiments the absorber 102 Isotope choice Inverted hierarchy - High isotopic natural

10 (meV) 10 abundance or enrichment β β m Exposure Normal hierarchy 0vββ favorite - Large active mass (M) 1 mechanism: detector Light Majorana neutrino - Long live-time exchange 10−1 10−1 1 10 102 mlightest (meV) 22 TheThe CUORECUORE detectorexperiment CUORE

From few g to 1 tonne TeO2 cryogenic calorimeters for double beta decay search

CUORE

Detectormass [kg] 4 crystal array

334 g

34 g 73 g

21 g Cuoricino 6 g MiDBD

Time from start [years] 23 CUOREThe CUORE optimization experiment

The CUORE experiment started taking data in 2017. CUORE First time such a large number of macro-bolometers (~ 1000) simultaneously operated in a completely new and unique cryogenic system Detector and overall system different compared to previous smaller scale bolometer experiments Dedicated detector characterization and optimization campaigns performed in order to characterize and improve the detectors and overall system performance. Goal: Improve the energy resolution and reach stable data-taking conditions - Characterization and tuning of detector operating parameters - Noise reduction

0.15 (mV) 14 0.9 350 SNR 1.4 Hz Bol 0.14 V

12 (mV) RMS and harmonics 0.13 0.8 300 10 0.12 0.7 Pulse Amplitude (V) Amplitude Pulse 250 8 0.11 0.1 0.6 6 200 0.09 4 0.5 150 0.08 2 0.07 0.4 100 0 0 10 20 30 40 50 60 70 80 90 IB (pA) 1000 2000 3000 4000 5000

VBias (mV) Load curves and — Vbol — PAmp Pulse Tubes active noise cancellation set detectors WP — RMS — SNR D'Addabbo A. et al.,Cryogenics 93, 55-56, (2018) https://doi.org/10.1016/j.cryogenics.2018.05.001 24 The CUORE experiment CUORE background budget CUORE

CUORE GOAL: 0.01 counts/keV/kg/y

Measured in CUORE-0 Preliminary

Material screening

C L limit 90% CL limit Value

LNGS ﬂux

counts/keV/kg/yr

25 CUORE sensitivity and perspectives CUORE CUORE 0vββ exclusion sensitivity in 5 years (90% C.L.):

S0v ~ 9 x 1025 yr with

3 3 -2 10 10 nominal background: 10 c/(keV⋅kg⋅yr) CUORE Preliminary Mo and Se Ge

2 CUORE limit (Te), PhysRevLett.124.122501 102 nominal energy resolution : 5 keV FWHM 10 Xe CUORE sensitivity (Te) in the Region Of Interest (ROI) Inverted hierarchy

10 10 (meV) β β Next generation of 0vββ decay experiments seek m CUPID sensitivity goal to be sensitive to the full Inverted Hierarchy region: Normal hierarchy 1 1 Sensitivity S0v ~1027 yr, mββ ~ 6 - 20 meV

Other isotopes −1 −1 10 10 CUPID (CUORE Upgrade with Particle ID) project: 10−1 1 10 1002 0.2 0.4 0.6 0.8 1 m (meV) build a future experiment with ~ 1500 enriched light lightest emitting bolometers mounted in the CUORE cryostat, reaching nearly zero background goal, Bkg < 10-4 c/(keV⋅kg⋅yr)