The start up of the CUORE experiment at LNGS CUORE Photo credit: - - PowerPoint PPT Presentation

CUORE

The start up of the CUORE experiment at LNGS

Antonio Branca @ INFN Padova On behalf of the CUORE Collaboration WIN2017 @ UC Irvine – 19-24 June 2017

Photo credit: Yury Suvorov

CUORE

Double beta decay (DBD)

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• proposed in 1935 by

Maria Goeppert-Mayer;

• 2nd order process allowed

in the Standard Model;

(A, Z) → (A, Z +2)+2e− +2ν (A, Z) → (A, Z +2)+2e−

τ >1024−25yr

• proposed in 1937 by

EKore Majorana;

• requires physics beyond

Standard Model;

τ ~1019−21yr

2ν DBD: 0ν DBD: 0ν DBD Signature: monochromaOc line in the energy spectrum at the energy value smeared by detector resoluOon! Energy spectrum of the two electrons in DBD

CUORE

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Double beta decay (DBD) II

(T 0ν

1/2)1 = G0ν(Q, Z) |M 0ν|2 |hmββi|2

m2

e

The 0ν DBD half-life:

Phase space factor ~Q5

ßß

(accurately calculable) Nuclear Matrix Element (theoreOcal uncertainty ~2-3) EffecOve Majorana mass

Ca

48

Ge

76

Se

82

Zr

96

Mo

100

Cd

116

Sn

124

Te

128

Te

130

Xe

130

Nd

150

|

ν

|M

1 2 3 4 5 6 7 8 9

ISM IBM QRPA-T QRPA-J PHFB GCM

Physics consequences if 0ν DBD is observed:

• proof of the Majorana nature of neutrino;
• constrain on the neutrino mass hierarchy and scale;
• lepton number violaOon (ΔL = 2): a possible source
• f maKer-anOmaKer asymmetry in the universe;

mββ = f (Δm1,2,Δm2,3,m1,α1,α2,δ)

CUORE

Sensitivity

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T

1/2 0ν

( )

• sens. ∝i.a.⋅ε ⋅

M ⋅t ΔE ⋅ B

Half-life corresponding to the minimum number of detectable signal events above background at a given C.L.

Isotopic abundance Detector efficiency Detector mass Measuring Ome (also “live Ome”) Energy resoluOon Background

In order to build a high sensiOvity experiment:

• select 0v DBD candidates with high natural isotopic abundance or enriched;
• high detector mass;
• good detector stability over a long period;
• extremely high energy resoluOon;
• extremely low background environment;

CUORE

Time [s] 0.5 1 1.5 2 2.5 3 3.5 4 Amplitude [mV] 1600 1800 2000 2200 2400 2600 2800 3000 3200

Bolometric technique in CUORE

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(A) Copper frame: 10 mK heat sink

(B) PTFE holders: weak thermal coupling (C) TeO2 crystal: energy absorber RadiaEon: energy deposit (E) NTD Ge thermistor: resisOve thermometer (D) Si joule heater: reference pulses

A B C D E readout Bolometer: detector and source

• f 0ν DBD. High efficiency and

resoluOon;

ΔT = E C(T) C(T) = T ϑ D ⎛ ⎝ ⎜ ⎞ ⎠ ⎟

3

@T =10mK ⇒ C ~10−9 J K ; ΔT = 0.1 mK MeV ; τ ~1s; ΔT

Low temperature needed:

CUORE

A rare event search

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Searching for a rare event (0ν DBD): ………………………

τ >1024−25yr

Extremely important to reduce as much as possible backgrounds:

• a. natural radioacOvity from outside the detector:
• cosmic ray muons induced background;
• neutron and gamma fluxes;
• b. natural radioacOvity from the detector itself:
• long-lived nuclei (40K, 238U, 232Th);
• anthropogenic radioacOve isotopes (60Co,

137Cs, 134Cs);

• cosmogenical radioacOve isotopes (60Co);

c. mechanical vibraOon noise:

• cryogenic system and seismic noise;

CUORE

CUORE installed @ LNGS

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CUORE @ Hall A

• average depth: ~3600 m.w.e.
• muon flux:

~3×10-8 μ/(s cm2)

• neutron flux:

< 4×10-6 n/(s cm2)

• gamma flux:

~0.73 γ/(s cm2)

CUORE

Suspension System

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Abatement of vibrations: detector mechanical decoupling from the outside environment:

• detector hung by the Y-Beam through

cables made of stainless steel tie bars, Kevlar ropes and copper bars (damping the horizontal oscillations);

• 3 minus-K springs connect the Y-Beam to

the Main Support Plate, MSP (attenuating the noise of ~35 dB);

• elastometers at the structure basis (seismic

isolators); Radioactive background reduction:

• outer neutron shield: polyethylene + borated

powder;

• outer gamma shield: lead shield;

Y-Beam Minus-K Elastometers Lead shield H3BO3 panels

Polyethylene

MSP

CUORE

Cryogenic System

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Specifics:

• Fast Cooling System: T down to ~40 K;
• 5 Pulse Tubes cryocooler: T down to ~4 K;
• Dilution Refrigerator: T operations 10 mK;
• Nominal cooling power: 3 µW @ 10 mK;
• Cryogen-free cryostat: high duty cycle;

Cool down ~15 tons @ T < 4 K and ~1.5 tons @ T = 10 mK in a few weeks. Radioactive background reduction:

• material screening and accurate selection

to ensure radiopurity;

• lead shielding (Roman and modern Pb);

CUORE

The CUORE “core”

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All 19 towers installed between July-August 2016 A single CUORE tower 988 TeO2 crystals arranged in 19 towers (13 floors - 52 crystals each):

• 130Te for 0v DBD: good Q-value

(2528 keV) in low β/γ region, high natural abundance (34.17%);

• total TeO2 mass of 742 kg (206

kg of 130Te); RadioacOve background reducOon:

• minimizaOon of material/

surface facing the crystals;

• developed a stringent protocol

for the tower assembly and material cleaning (tested on predecessor CUORE-0);

CUORE

CUORE0: the first CUORE tower

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First detector tower built using the new techniques and assembly line developed for CUORE:

• operated from 2013 to 2015 in old Cuoricino cryostat;
• proof of concept for CUORE;
• 0ν DBD search by itself;

Reconstructed Energy (keV) 2470 Events / (2 keV) χ2/NDF = 43.9/46 Event Rate (counts/(keV kg yr)) 2480 2490 2500 2510 2520 2530 2540 2550 2560 2570 0.05 0.1 0.15 0.2 0.25 2 4 6 8 10 12 14 16 18 Residual (σ)

–4 –2 2 4

Reconstructed Energy (keV) 2560 2570 2580 2590 2600 2610 2620 2630 2640 2650 Counts / (0.5 keV) 1 10

2

10

3

10

4

10

Summed calibration data Projected fit γ Tl

208

escapes Te X-ray

) σ Residual (

6 − 4 − 2 − 2 4 6

RESULTS: Ø 0νββ upper limit: T1/2(0ν) > 4×1024 yr (@ 90% C.L.) combined CUORE0 + Cuoricino results; ü ROI background: 0.058 ± 0.004 c/(keVŸkgŸyr); ü ResoluOon: 5.1 ± 0.3 keV FWHM @ 2615 keV; ResoluOon consistent with the CUORE goal of 5 keV.

CUORE

Material cleaning and assembling

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Production of the TeO2 crystals:

• by Shanghai Institute of Ceramics, Chinese Academy
• f Science (SICCAS);
• two successive crystal growths starting from high

purity synthetized TeO2 powder;

• cutting, orienting and shaping from raw ingots and

surface polishing and packaging;

• all operations performed in a dedicated clean room

and following strict controls to limit radioactive contamination; Cleaning of copper surfaces (tower parts and 10 mK cryostat shield):

• new cleaning techniques developed at LNL;
• tumbling, electropolishing, chemical etching,

magnetron plasma aimed at the removal of a thin layer of material (from 1 µm to 100 µm);

CUORE

Material cleaning and assembling

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Strict protocol adopted for each step of the CUORE towers construction: all in N2 atmosphere and within glove boxes to avoid radioactive recontamination;

• 1. sensors gluing
• 2. tower assembly
• 3. wire bonding
• 4. tower storage

CUORE

β/γ dominated α dominated

208Tl 190Pt 238U 234U/226Ra/230Th 210Po 222Rn 218Po

Background reduction effectiveness

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Comparison of the background in Cuoricino and CUORE-0

0ν DBD region (2.47-2.58 MeV) α region (2.7-3.9 MeV) Cuoricino 0.169 ± 0.006 0.110 ± 0.001 CUORE-0 0.058 ± 0.004 0.016 ± 0.001

Background indexes (counts/(keV•kg•yr))

• Material cleaning: 238U and 232Th α

lines reduced (~ factor of 7);

• Tower assembly in N2 atmosphere:

238U γ lines reduced (~ factor 2/3);

• Same Cuoricino cryostat: 232Th γ lines

not reduced;

CUORE

CUORE background projection

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Main background index in the 0ν DBD region expected for the various components of CUORE

Measured in CUORE-0 Material screening

LNGS Fluxes

Preliminary expected dominant contribuOon from the Cu of the towers structure Projected total BI in the 0ν DBD region is consistent with CUORE background goal (10-2 counts/(keV•kg•yr)): BI = (1.02 ± 0.03(stat.)−0.10

+0.23(syst.))⋅10−2

counts kev⋅kg⋅ yr (Preliminary)

CUORE

Cryostat commissioning

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300 K 40 K 4 K 600 mK 50 mK 10 mK Commissioning completed in March 2016:

• stable base T = 6.3 mK over 70 days (no

detector, full load);

• full detector read-out chain (electronics, DAQ)

test, temperature stability with Mini-Tower (8 crystal tower); Mini-Tower resoluOon without noise opOmizaOon.

CUORE

CUORE Installation

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Towers installaOon completed 10 mK Cu shield closed Lead shield installed Cables rouOng Sep – Nov 2016 Aug 2016 Cryostat closed Nov 2016

CUORE

CUORE cooldown and commissioning

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• cooldown started on Dec 5, 2016;
• lasted about 3.5 weeks (without taking

into account technical stops for system debugging);

• n Jan 26, 2017 reached a base

temperature of T = 7 mK;

Time 12/05-12:16 12/22-14:10 01/08-16:04 01/25-17:59 T (K) 10

2

10

Diode thermometer at 10mK plate

cryogenics debugging electronics debugging

First pulse observed on Jan 27, 2017

A•er the cooldown started a phase of detector opOmizaOon

CUORE

CUORE status

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Noise opOmizaOon:

• electronic noise aKenuaOon;
• reducOon of mechanical vibraOon;
• tuning of the pulse tube relaOve phase

shi•ing; Temperature scan:

• scan around the base temperature (Tbase)

to choose the value opOmizing the signal and to set the design thermistors’ value

• f the resistance;

Working point measurement:

• current bias (IB) scan to choose the value

maximizing the SNR for each thermistor at the given Tbase; Commissioning of the analysis so•ware;

Rth = R0e

T0 Tbase = Vth

IB

“Neutron TransmutaOon Doped” (NTD) Germanium thermistors to read-out the crystals Preliminary CUORE started taking data on April 2017

CUORE

Projected exclusion sensitivity

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• Bayesian fit on toy MC background

spectra;

• exclusion sensiOvity obtained from

the distribuOon of the 90% C.I. limits

• n T0ν

1/2 for the toy MC experiments

for each fixed live Ome;

• values of the BI projecOon for CUORE

and energy resoluOon from CUORE-0 have been considered as input for the computaOon; RESULTS: ü expected to reach CUORE-0 + Cuoricino sensiOvity in few days; ü expected exclusion sensiOvity of T0ν

1/2~ 9×1025 yr (90% C.I.) in 5 years of live Ome;

Preliminary

CUORE

Conclusion

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• November 2016: installaOon

completed;

• Dec 2016 – Jan 2017: successful

cooldown of the detector;

• 27 Jan 2017: first CUORE pulse;
• Feb – Apr 2017: commissioning
• f the detecor;
• April 2017: CUORE started taking

data; Thank you for your aKenOon!

CUORE

Additional material

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CUORE

List of useful papers

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CUORE CollaboraOon results in this presentaOon:

• ProducOon of high purity TeO2 single crystals for the study of neutrinoless

double beta decay, J. Cryst. Growth 312 (2010) 2999-3008;

• ValidaOon of techniques to miOgate copper surface contaminaOon in CUORE,
• Astropart. Phys. 45 (2013) 13-22;
• Search for Neutrinoless Double-Beta Decay of Te-130 with CUORE-0, Phys. Rev.
• LeK. 115, 102502 (2015);
• Analysis Techniques for the EvaluaOon of the Neutrinoless Double-β Decay

LifeOme in Te-130 with CUORE-0, Phys. Rev. C 93, 045503 (2016);

• The projected background for the CUORE experiment, arXiv:1704.08970;
• CUORE SensiOvity to 0νββ Decay, arxiv:1705.10816;

CUORE

Projected discovery sensitivity

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• Bayesian fit on toy MC background

spectra;

• discovery sensiOvity obtained from

T0ν

1/2 for which the posterior probability

• f the background only hypothesis

given the data is smaller than 0.0027 (i.e. 3σ) in 50% of the experiments;

• values of the BI projecOon for CUORE

and energy resoluOon from CUORE-0 have been considered as input for the

• computaOon. Also a worse scenario,

with 10 keV FWHM, has been considered; RESULTS @ 5 keV FWHM: ü expected to have a discovery sensiOvity greater than CUORE-0 + Cuoricino limit in less than one month; ü expected discovery sensiOvity of T0ν

1/2~ 4×1025 yr (3σ) in 5 years of live Ome;

Preliminary

CUORE

Detector Calibration System

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300 K 40 K 4 K 600 mK 50 mK 10 mK Lead shielding Detector towers 4 K Thermalizer Source string location before calibration (Motion Box) Stainless steel bellows Inner guide tube route Outer guide tube route Detector region guide tube 59 mm 6 mm

Kevlar string Thoriated tungsten (calibration source) Copper capsule PTFE heat shrink tubing

~9.2 mm 8 mm

• Bolometers require independent in situ energy calibration;
• For CUORE, we use:
• 232Th γ-ray sources every ~month (239 keV to 2615 keV);
• Constant-energy pulsers to measure detector stability and

correct for variations in detector gain;

• Sources are outside cryostat during physics data-taking and

lowered into cryostat and cooled to 10 mK for calibration;

• Sources are put on strings and are lowered under their own

weight;

• A series of tubes in the cryostat guides the strings;

CUORE

mββ sensitivity and limits

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[meV]

lightest

m

1 −

10 1 10

2

10 [meV]

β β

m

1 −

10 1 10

2

10

3

10

CUORE-0 + Cuoricino limit (Te) CUORE sensitivity (Te) Normal hierarchy Inverted hierarchy

1 10

10

10

Other isotopes Mo Ge Xe

Assuming:

• BI = 0.01 counts/(keV•kg•yr);
• energy resoluOon of 5 keV FWHM;
• 5 years live Ome;

CUORE expected sensiOvity to mββ is:

mββ < 50 −130 meV

CUORE

130Te for 0ν DBD

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Isotopic Abundance [atomic %]

5 10 15 20 25 30 35

Q-value [keV]

1000 1500 2000 2500 3000 3500 4000 4500

Ca

48

Ge

76

Se

82

Zr

96

Mo

100

Cd

116

Sn

124

Te

128

Te

130

Xe

136

Nd

150

• good Q-value (2528 keV) in low β/γ region;
• high natural abundance (34.17%);

CUORE

Roman Lead

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• Ancient Roman lead bricks for

low-activity shielding;

• Recovered in late ‘80s from

shipwreck off Sardinian coast;

• Obtained through agreement

between INFN and Italian historical society;

• 270 bricks, 33 kg each = 7 tons

(after inscriptions removed);