Performance of the CUORE bolometers · CUORE I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15...

CUORE

I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15 Set. 2017

Performance of the CUORE bolometers

- First CUORE results -

I.NutiniGran Sasso Science Institute

INFN Laboratori Nazionali del Gran Sasso on behalf of the CUORE collaboration

103° Congresso Nazionale della Società Italiana di FisicaTrento - Povo, 11-15 settembre 2017

1

CUORE

2I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15 Set. 2017

CUORE - Cryogenic Underground Observatory for Rare Events Primary goal: Search for neutrino-less double beta (0νββ) decay of 130Te

The CUORE experiment and the 0vββ search

Why 130Te:• Large transition energy:

Qββ (130Te) = 2527.5 keV • Highest natural isotopic abundance

(η = 33.8%) • 130Te within the detector absorber of TeO2

(high detection efficiency ε) • Reproducible growth of large number of

high quality crystals (M)

S

0⌫(n�) = ln2 ✏

1

n�

x ⌘ NA

MA

rM T

B �

Experimental 0vββ detection sensitivity:

- Lepton number violation process (BSM) - Majorana nature of neutrino - Constraints on neutrino mass hierarchy and scale - Not yet observed T0v > 1024-25 yr

https://en.wikipedia.org/wiki/V

DetectorTowers

Top LeadShieldSide LeadShield

300 K

40 K

4 K

StillHeat Exchanger

Mixing Chamber

Bottom LeadShield

Plates :

CUORE



• Closely packed array of 988 TeO2 crystals (19 towers of 52 crystals 5×5×5 cm3, 0.75 kg each) High Mass of TeO2: 742 kg (206 kg of 130Te ) and high granularity

• Low background: - Deep underground location (Gran Sasso National Labs - LNGS), - Strict radio-purity controls on materials

and assembly, - Passive shields (Pb) from external and cryostat radioactivity Background aim: 10-2 c/(keV⋅kg⋅yr)

• Low vibrations - Multistage cryogen-free cryostat: - Mass to be cooled down: ~15 tonnes (Pb, Cu and TeO2) - TeO2 detectors operating temperature: ~10 mK Energy resolution aim: 5 keV FWHM in the Region Of Interest (ROI)

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

The CUORE challenge:


CUORE


CUORE TeO2 bolometers

CUORE module: a tower

CUORE 19 towers array52 (nat)TeO2 crystals Absorber = 0vββ source

1 Ge NTD thermistor for each crystal

1 Si heater for each crystal <— Cu frames and PFTE holders Cu-PEN cables —>


CUORE


CUORE cooldown and data-takingCryogenic infrastructure and auxiliary systems

Detector Calibration System12 232Th γ-ray sources (thoriated tungsten) are cooled to base temperature and lowered into the experimental volume for calibration

Shieldings- External lead shielding and concrete support structure - Internal Ancient Roman Lead Shield (6 cm thick, 5 tons) @ 4K - Internal Top Lead Shield (30 cm thick, 2.5 tons) @ 50 mK

Multistage cryogen-free cryostat: - Fast Cooling System- 5 Pulse Tube cryocoolers (down to 4 K) - Continuous-cycle 3He/4He dilution refrigerator (down to base temperature ~10 mK)

35 K

4 K

Still 800 mK

Heat exchanger 50 mK

Mixing chamber10 mK

Roman lead shield @4 K

CUORE


CUORE cooldown and data-taking

27.01.2017 the first CUORE pulse!

- Cryogenic system commissioning : completed in Feb.2016 - Detector assembly and installation: completed at the end of Aug. 2016 - Detector cooldown: Started at the beginning of Dec. 2016, Cooldown time: ~ 20 days down to ~3.4 K, vacuum pumping into the inner volume, ~ 1.5 days down to ~ 10 mK

Observed first detector pulses just after the cool down without any optimization

CUORE


Detector characterization and first physics resultsDetector pre-operations and optimization phase (January-March 2017):

Noise optimization: • Electronics noise attenuation • Vibrations reduction (detector must be mechanically isolated) • Pulse tube relative phase shift tuning

Temperature scan: Temperature scan around base temperature to choose the one that optimizes the signal and at the same time allows to work with the designed NTD resistance. Selected working temperature: 15 mK

Setting the working points: Load curves scan to choose the best bias voltage to feed each channel’s NTD: • linear behavior for small temperature variations • maximization of signal to noise ratio • optimization of pulse amplitude

CUORE


Detector characterization and first physics results

Science operations started on April 14, 2017 • First short dataset: test data processing tools and

re-optimization of the detector working points • Second dataset: 3 weeks of physics data

bracketed by an initial and a final calibration (May 4 - June 11) —> First CUORE physics results

• Second optimization campaign and new dataset - physics runs - ongoing from August

CUORE science runs (from April 2017)

Operational performance- 984/988 operational channels - Excellent data-taking efficiency - Improved detector stability - 899/984 best performing channels used for initial analysis

Acquired statistic for 0νββ decay search

natTeO2 exposure: 38.1 kg yr

130Te exposure: 10.6 kg yr

May

June

2017Second Dataset - Time breakdown

65.4 %

21.8 %

9.4 %3.3 %

Physics CalibrationOther Test

CUORE Preliminaryyr⋅Exposure: 38.1 kg


Run Time Breakdown

Energy [keV]500 1000 1500 2000 2500

Phys

ics e

vent

rate

[cou

nts /

(keV

kg

yr)]

3−10

2−10

1−10

1

10

CalibrationPhysics


CUORE



Calibration and Background spectra

Calibration: 232Th sources deployed inside the CUORE detector Background - Physics: Spectrum is consistent with the background expectations

Cumulative energy spectrum from all the channels selected for the 0vββ initial analysis


Energy [keV]2560 2580 2600 2620 2640 2660 2680

Even

ts [c

ount

s / 0

.5 k

eV]

0

2000

4000

6000

8000

10000

12000 CUORE Preliminaryyr⋅Exposure: 38.1 kg

Energy [keV]2570 2580 2590 2600 2610 2620 2630 2640 2650 2660

]σ

Resid

ual [

2−1−0123

Energy [keV]2570 2580 2590 2600 2610 2620 2630 2640 2650 2660

Even

ts [c

ount

s / 2

keV

]

05

10152025303540 CUORE Preliminary

yr⋅Exposure: 38.1 kg

CUORE



Calibration and Background spectra

• Average (“harmonic mean”) energy resolution in calibration runs: 10.6 keV FWHM @ 2615 keV

• Significantly better performance in physics data (7.9 ± 0.6) keV FWHM @ 2615 keV

Detector performance - Energy resolution @208Tl decay gamma-peak:

Energy [keV]2480 2500 2520 2540 2560

]σ

Resid

ual [

2−1−0123

Energy [keV]2480 2500 2520 2540 2560

Even

ts [c

ount

s / 2

.5 k

eV]


yr⋅Exposure: 38.1 kgCUORE Preliminary










CUORE


Detector characterization and first physics results0νββ analysis

Energy [keV]2400 2450 2500 2550 2600 2650 2700

Eve

nts [

coun

ts / k

eV]

02468

1012141618 Blinded

UnblindedTl208

Bi214 Co60


Fit to evaluate best fit decay rate for 130Te: Simultaneous unbinned extended maximum likelihood fit - ROI region: [2465,2575 keV] around Qββ (130Te). - Events selection efficiency: (62.6 ± 3.4)% - ROI background index:

(9.8–1.5+1.7) × 10-3 c/(keV⋅kg⋅yr)

Considering the overall 0νββ signal efficiency: (55.3 ± 3.0)% - Best fit decay rate: (-0.03–0.04+0.07(stat.) ± 0.01 (syst.)) × 10-24/yr

Half-life limit (90%C.L including syst.): T0ν (130Te) > 4.5 x 1024 yr

CUORE



Combined fit: CUORE + CUORE-0 + Cuoricino

Exposure 130Te: 19.75 kg·yr Cuoricino, 9.8 kg·yr CUORE-0, 10.6 kg yr CUORE

Bayesian half-life limit (90% CL) T0ν (130Te) > 6.6 × 1024 yr

Limit on mββ: mββ < 210 - 590 meV

[meV]lightestm1−10 1 10 210

[meV

]ββ

m

1−10

1

10

210

310

(Preliminary)Cuoricino + CUORE-0 + CUORE limit (Te)

CUORE sensitivity (Te)

Normal hierarchy

Inverted hierarchy

0 0.2 0.4 0.6 0.8 1

1−10

1

10

210

310

Other isotopes

Mo

Ge

Xe

0νββ analysis

1

T 0⌫1/2

/ G(Q�� , Z)|Mnucl|2|m�� |2Effective neutrino mass term

CUORE


Conclusions

CUORE is the first tonne-scale bolometric 0νββ detector. First months of CUORE operations: • First CUORE physics results of T0ν in 130Te after 3 weeks of data taking • Exceptional cryostat performance and important information on

detectors characterization, noise, resolutions and background levels. • Detector optimization campaign focused on improving the resolution

through further noise reduction • Data taking has restarted at the end of July 2017, physics runs

ongoing • More to come!

CUORE


Thank you on behalf of The CUORE collaboration

CUORE


Backup

CUORE



Double beta decay is a very rare nuclear decay (N,Z) → (N-2, Z+2)

2vββ: - 2nd order process allowed in SM - Observed in several nuclei: !~1019-21 y 0vββ: - Lepton number violation process (BSM) - Majorana nature of neutrino - Constraints on neutrino mass hierarchy and scale - Not yet observed !>1024-25 y 2vββ

0vββ 1

T 0⌫1/2

/ G(Q�� , Z)|Mnucl|2|m�� |2

Phase space integral Nuclear matrix elementEffective neutrino mass termm�� = |⌃im⌫iU

2ei|

Q�� Q-value of the ββ decay






CUORE


CUORE TeO2 bolometersBolometer principle of operation

Heat bath ~ 10 mK

(copper)

Thermal coupling

(PTFE)

Thermistor

(NTD-Ge)

Absorber Crystal

(TeO2)

Absorber crystal (nat)TeO2 : 0vββ source

C(T) ~ 2 x 10-9 J/K (@ 10 mK) Thermistor NTD-Ge

Rwp ~ 10-100 MΩ

∆T

⌧

R(T ) = R0exp(T0T )1/2

C(T ) / T 3 Lattice specific heat

�T / Edep

C⇡ 100µK

MeV

Simplest thermal model: One thermal capacity (crystal)One thermal link G (btw crystal/heat bath)

Amplitude of the pulse ∝ Energy deposit

⌧ =G

C⇡ 1s


CUORE


CUORE cooldown and data-takingCryogenic infrastructure and auxiliary systemsMultistage cryogen-free cryostat: - Fast Cooling System- 5 Pulse Tube cryocoolers (down to 4 K) - Continuous-cycle 3He/4He dilution refrigerator (down to base temperature ~10 mK)

35 K

4 K

Still 800 mK

Heat exchanger 50 mK

Mixing chamber10 mK

FCSPT

CUORE


CUORE cooldown and data-takingCryogenic infrastructure and auxiliary systems

Cryostat support structure

CUORE


Detector characterization and first physics resultsDataset 2: Calibration spectrum - Line shape

Calibration: 232Th sources deployed inside the CUORE detector

Energy [keV]2560 2580 2600 2620 2640 2660 2680

Even

ts [c

ount

s / 2

keV

]

1

10

210

310



Tower 4 Fit components: • a flat background • a step-wise smeared background • a double gaussian for the main

peak • a combination of gaussian

escape lines

Fit on a tower by tower basis

Energy [keV]500 1000 1500 2000 2500

Even

t rat

e [c

ount

s / (k

eV k

g yr

)]

3−10

2−10

1−10

1

10

CUORE-0CUORE

Ac228 Co60Co60

K40

Bi214

Tl208

Bi214

Bi214

Tl208


CUORE


Detector characterization and first physics resultsDataset 2: Background spectrum

Background - Physics: Significant reduction in the γ region with respect to CUORE-0 (CUORE-like tower experiment), Spectrum is consistent with the background expectations

CUORE


Detector characterization and first physics resultsDataset 2: Background spectrum - Blinding

Blinding procedure: • Randomly move a fraction of events from

+/- 20 keV of 2615 keV to the Q-value and vice versa

• The blinding algorithm produces an artificial peak around the 0νDBD Q- value and blinds the real 0νDBD rate of 130Te.

• When all data analysis procedures are fixed the data are eventually unblinded Energy [keV]

2400 2450 2500 2550 2600 2650 2700

Eve

nts [

coun

ts / k

eV]

02468

1012141618 Blinded

UnblindedTl208

Bi214 Co60


Energy [keV]2480 2500 2520 2540 2560

]σ

Resid

ual [

2−1−0123

Energy [keV]2480 2500 2520 2540 2560

Even

ts [c

ount

s / 2

.5 k

eV]












CUORE


Detector characterization and first physics resultsDataset 2 : 0νββ analysis

Energy [keV]2400 2450 2500 2550 2600 2650 2700

Eve

nts [

coun

ts / k

eV]

02468

1012141618 Blinded

UnblindedTl208

Bi214 Co60


ROI Fit to evaluate best fit decay rate for 130Te: Simultaneous unbinned extended maximum likelihood fit ROI region: [2465,2575 keV] around Qββ (130Te). The fit has 3 components: • a posited peak at the Q-value of 130Te • a floating peak to account for the 60Co sum gamma line (2505 keV)• a constant continuum background, attributed to multi scatter Compton events from 208Tl and surface alpha events

- Overall signal efficiency: (55.3 ± 3.0)% - ROI background index: (9.8–1.5+1.7) × 10-3 c/(keV⋅kg⋅yr) - Half-life limit (90%C.L including syst.): T0ν (130Te) > 4.5 x 1024 yr

]-1 yr-24Decay rate [100.1− 0 0.1 0.2 0.3 0.4 0.5 0.6

NLL

02468

101214161820

CuoricinoCUORE-0CUORECUORE + CUORE-0 + Cuoricino


]-1 yr-24Decay rate [100.1− 0 0.1 0.2 0.3 0.4 0.5 0.6

NLL

0

2

4

6

8

10

12

14 CUORE (stat. only)

CUORE (stat. + syst.)


CUORE


Detector characterization and first physics resultsDataset 2: Background spectrum - NLL FITBest fit decay rate (-0.03–0.04+0.07 (stat.) ± 0.01 (syst.)) × 10-24 / yr

Bayesian Half-life limit (90%C.L including syst.): T0ν > 4.5 x 1024 yr

Median expected sensitivity based on actual exposure: S0ν > 3.6 × 1024 yr (with sensitivity paper technique) S0ν >3.3 × 1024 yr (with same fit technique as ROI fit)

Combined fit: CUORE + CUORE-0 + Cuoricino Bayesian half-life limit (90% CL) T0ν > 6.6 × 1024 yr

CUORE



CUORE GOAL: 0.01 counts/keV/kg/y

CL limit 90% Value

counts/keV/kg/yr

LNGS flux

Material screening

Measured in CUORE-0

Preliminary

CUORE background budget

CUORE


The CUORE collaboration

Performance of the CUORE bolometers · CUORE I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15...

Documents

Transcript of Performance of the CUORE bolometers · CUORE I.Nutini, GSSI - INFN LNGS; 103° Congresso SIF, 15...