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CUORE: the first bolometric experiment at the ton scale for CUORE rare decay searches Antonio Branca DFA Universit degli Studi di Padova & INFN Sezione di Padova On behalf of the CUORE Collaboration PM2018 14 th Pisa Meeting on

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SLIDE 1

CUORE

CUORE: the first bolometric experiment at the ton scale for rare decay searches

Antonio Branca – DFA Università degli Studi di Padova & INFN Sezione di Padova On behalf of the CUORE Collaboration PM2018 – 14th Pisa Meeting on Advanced Detectors, 30 May 2018

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SLIDE 2

CUORE

To build a high sensitivity experiment:

  • 𝒋. 𝒃.: select 0v DBD candidates with high natural

isotopic abundance or enriched;

  • 𝜻: high detection efficiency;
  • 𝑵: high detector mass;
  • 𝒖: good detector stability over a long period;
  • 𝜠𝑭: extremely high energy resolution;
  • 𝑪: extremely low background environment;

The signal CUORE is searching for

Energy spectrum of the two electrons in the final state

T

1/2 0ν

( )

  • sens. ∝i.a.⋅ε ⋅

M ⋅t ΔE ⋅ B

  • A. Branca - PM2018

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SLIDE 3

CUORE

2 4 6 8 10 Time (s) 0.2 0.4 0.6 0.8 1 Amplitude (a. u.)

Bolometric technique in CUORE

(A) Copper frame: 10 mK heat sink (B) PTFE holders: weak thermal coupling (C) TeO2 crystal: energy absorber Radiation: energy deposit (E) NTD Ge thermistor: resistive thermometer (D) Si joule heater: reference pulses

A B C D E Readout

ΔT = E C(T) C(T) = T ϑ D ⎛ ⎝ ⎜ ⎞ ⎠ ⎟

3

ΔT Low temperature needed: @𝑼 = 𝟐𝟏 𝒏𝑳

  • high efficiency;
  • excellent energy resolution;
  • large masses achievable;
  • 130Te high natural isotopic

abundance;

  • 130Te Q-value 2528 keV;

𝐷~1067 𝐾 𝐿 ; ∆𝑈 = 0.1 𝑛𝐿 𝑁𝑓𝑊 ; 𝜐~1𝑡

  • A. Branca - PM2018

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SLIDE 4

CUORE

CUORE installed @ LNGS underground laboratories (~3600 m.w.e.)

A rare event search

Searching for a rare event (0ν DBD): 𝜐 > 10DE6DF 𝑧𝑠 ………………………

Extremely important to reduce as much as possible backgrounds:

REDUCTION

  • Strict protocols for crystal

production @ SICCAS;

  • Cleaning techniques developed @

LNL for copper parts near crystals;

  • Strict protocol for assembling and

installation;

Suspension/damping systems and new noise cancellation tools

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

isotopes (60Co, 137Cs, 134Cs);

  • cosmogenic radioactive isotopes (60Co);

c. mechanical vibration noise:

  • cryogenic system and seismic noise;

REDUCTION REDUCTION

  • A. Branca - PM2018

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SLIDE 5

CUORE

Cryogenic system

Challenging task: cool down ~15 tons @ T < 4 K and ~1.5 tons @ T = 10 mK in a few weeks in a low radioactive environment.

  • Cryogen-free (dry) cryostat: high duty cycle:

Ø Fast Cooling System (4He gas): T down to ~40 K; Ø 5 Pulse Tubes (PTs) cryocoolers: T down to ~4 K;

  • (Custom) Dilution Refrigerator: T operations 10 mK;
  • Nominal cooling power: 3 μW @ 10 mK;

Reduction of radioactive background (from detector):

  • material screening and accurate selection to ensure

radiopurity (mainly pure copper, other material in small amount, limited amount of Multi Layer Insulator);

  • lead shielding (Roman and modern Pb);
  • A. Branca - PM2018

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SLIDE 6

CUORE

Cryostat commissioning

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);

  • successful deployment of the calibration sources at base

temperature; System ready for detector installation.

No noise

  • ptimization
  • A. Branca - PM2018

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SLIDE 7

CUORE

Detector assembling and installation

Assembling: in N2 atmosphere and within glove boxes to avoid radioactive recontamination (between 2013 and 2014);

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

Installation: protected area inside clean room flushed with radon free air; protective bags flushed with N2 for

  • vernight

and emergency storage (started after cryostat commissioning); Strict protocol adopted for each step of assembling/installation (developed and tested in predecessor experiment CUORE0):

  • A. Branca - PM2018

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SLIDE 8

CUORE

The CUORE “core” installed

All 19 towers installed between July-August 2016

Design specifics:

  • detector arrangement: 19 towers with 13 floors of 4 crystals each;
  • crystals: 988 crystals, 5 cm3, 750 g each;
  • total TeO2 mass of 742 kg;
  • total 130Te mass of 206 kg (all natural abundance);

Reduction/control of radioactive background:

  • minimization of material/surface facing the crystals;
  • closely packed crystal array with high granularity;

GOALS:

  • low background of 106D 𝑑/(𝑙𝑓𝑊 M 𝑙𝑕 M 𝑧𝑠);
  • energy resolution: 5 𝑙𝑓𝑊 𝐺𝑋𝐼𝑁 in the Region Of Interest (ROI);
  • 0v-DBD projected sensitivity: 𝑈

T/D UV = 9 M 10DX 𝑧𝑠 (5 years, 90% C.L.);

  • A. Branca - PM2018

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SLIDE 9

CUORE

Detector cool down

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 noise studies ∆t [d]

0.5 1 1.5 2 2.5 3 3.5 4

T [K]

0.01 0.1 1 10 Still plate HEX plate MC plate CUORE cool down

Start: 2017-01-23 10:00

Last 4 days of cooldown: DU switched on

  • cooldown started on Dec 5, 2016: lasted ~26 days (without

counting technical stops for system debugging);

  • n Jan 26, 2017 reached a stable base temperature of T = 7 mK;

After the cooldown started an important phase of detector

  • ptimization alternated to data-

taking periods

After towers installation, the cryostat was closed between September-November 2016:

  • A. Branca - PM2018

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SLIDE 10

CUORE

Temperature (mK) 11 12 13 14 15 16 17 18 19 FWHM (keV) 2 4 6 8 10 12

FWHM Tl 2615 keV FWHM AC 911 keV

FWHM vs Temperature - Tl (2615 keV) and Ac (911 keV) peaks - October 2017 Temperature Scan

Setting the best working temperature

Temperature scans around base temperature to optimize detector resolution and NTDs resistances at design values (~100 𝑁Ω):

  • First scan (March 2017): identified the best working temperature of 15 mK (indications of better resolution at

lower T, but higher NTDs resistances then design values);

  • Second scan (July 2017): check setting from the first scan before starting of new data-taking;
  • Third scan (September 2017): with calibration sources deployed, confirmed trend of better resolution on physics

events at lower T. Set 11 mK as new working temperature;

Baseline and Pulser resolutions (from July 2017 scan) Resolutions

  • n physics

events (from September 2017 scan) CUORE Preliminary CUORE Preliminary

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SLIDE 11

CUORE

1000 2000 3000 4000 5000 PhaseID

1 −

10 1

ph

Median Normalised Noise A

Minimization of vibrational noise

Developed tool to minimize vibrational noise from PTs:

  • use linear drives (LD) to control PTs’ rotating valves;
  • PTs phase scan to find the configuration of minimum

noise across the whole detector; median

  • verall

channels vs PTs phase configuration PT induced noise on each channel vs PTs phase configuration 10 mK temperature: before and after LD switch on

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SLIDE 12

CUORE

Maximize SNR

Once the NTD resistances have been set by selecting the working temperature, the correct bias currents 𝐽[\]^ supplied to the thermistors have been optimized with dedicated measurements:

For each bolometer measured:

  • characteristic I-V curve: set bias currents lower than values at inversion point (avoid distorted signal shapes);
  • reference pulses amplitude, noise RMS and SNR at each (I,V) point: set bias current maximizing SNR;

1 2 3 4 5 Time (s) 0.2 0.4 0.6 0.8 1 Amplitude (a. u.) AP with pulser amplitude at 2200 AP with pulser amplitude at 1800 AP with pulser amplitude at 1200 AP with pulser amplitude at 500

Example of I-V (Load-Curve) for a channel Reference pulses for different amplitudes @ 𝐽[\]^ CUORE Preliminary

CUORE Preliminary

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SLIDE 13

CUORE

Data taking for physics analysis

Detector optimization ended in April 2017 to start science runs:

  • Dataset 1: 3 weeks of data bracketed by 2 calibration periods (May - June 2017). TeO2 exposure 37.6 𝑙𝑕 M 𝑧𝑠;

Ø still room for performance improvements;

Dataset 1 Dataset 2 Improved resolution between the two datasets Detector optimization restarted in July 2017:

ü careful investigation/upgrades to the electronics grounding in the CUORE Faraday cage; ü Introduced PTs phase scans to refine the abatement

  • f induced noise;

ü

  • ptimization of the operating temperature and

detector working points; ü software and analysis upgrades;

After the second optimization phase, resumed data-taking:

  • Dataset 2: same procedure as first dataset (August –

September 2017). TeO2 exposure 48.7 𝑙𝑕 M 𝑧𝑠;

  • A. Branca - PM2018

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SLIDE 14

CUORE

0.1 − 0.05 − 0.05 0.1 0.15 0.2 0.25 0.3 )

  • 1

yr

  • 24

Decay rate (10 2 4 6 8 10 12 14 16 18 20 NLL

CUORE CUORE-0 Cuoricino CUORE + CUORE-0 + Cuoricino

CUORE Preliminary

yr ⋅ Exposure: 86.3 kg

12 14 16

CUORE

yr ⋅ Exposure: 86.3 kg

  • Phys. Rev. Lett. 120, 132501 (2018)

0𝜉𝐸𝐶𝐸: fit results and half-life limits

Signal decay rate best-fit: Γ

UV = −16U.i jU.E (𝑡𝑢𝑏𝑢. ) ± 0.1 𝑡𝑧𝑡𝑢.

×106DX𝑧𝑠6T Background index best-fit (datasets average): 𝐶𝐽 = 0.014 ± 0.002 𝑑𝑝𝑣𝑜𝑢𝑡/(𝑙𝑓𝑊 M 𝑙𝑕 M 𝑧𝑠) Fit in the region of interest (2465-2575 keV) Profile negative-log-likelihood curves

2480 2500 2520 2540 2560

) σ Residual (

2 − 1 − 1 2 3

Reconstructed Energy (keV) 2480 2500 2520 2540 2560 Counts / (2.5 keV) 2 4 6 8 10 12 14 16

Co

60 β β

Q

CUORE

yr ⋅ Exposure: 86.3 kg

  • Phys. Rev. Lett. 120, 132501 (2018)

Combined (CUORE+CUORE0+Cuoricino) limit

  • n the half-life:

𝑈

T/D UV > 1.5 ⋅ 10DX 𝑧𝑠 (90% 𝐷. 𝑀. )

Effective Majorana mass limit: 𝑛vv < 110 − 520 𝑛𝑓𝑊

  • A. Branca - PM2018

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SLIDE 15

CUORE

𝑁x = 5 𝐻𝑓𝑊 𝑁x = 10 𝐻𝑓𝑊 𝑁x = 20 𝐻𝑓𝑊 𝑁x = 50 𝐻𝑓𝑊 𝑁x = 100 𝐻𝑓𝑊

Trigger thresholds & other searches

Expected WIMP modulation amplitude (max – min) in TeO2 for 𝜏{| = 106X𝑞𝑐 Projected 90% C.L. sensitivity on the spin- independent elastic WIMP-nucleon cross section

Could CUORE search also for very low energy events (like Dark Matter induced signals)?

CDMS Lite CRESST-II XMASS LUX

  • A. Branca - PM2018

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SLIDE 16

CUORE

Raw data Filtered data

Trigger thresholds & other searches

Lower the trigger thresholds for low energy event tagging:

Ø currently working on testing a trigger based on the Optimal Filter technique (Optimum Trigger); Current trigger thresholds ranging from 20 keV to ~100 keV. How to lower them? Matched filter technique: transfer function maximizing SNR (applied in frequency domain)

  • filtered pulses are less noisy;
  • lower thresholds could be achievable;

100 200 300 400 500 600 700 800 Energy (keV) 10 20 30 40 50 60 70 Channels

analysis threshold 90% trigger efficiency threshold

Distribution of 90% Trigger Efficiency Thresholds

CUORE Preliminary DS 2 CUORE Preliminary DS 2

CUORE0

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SLIDE 17

CUORE

Trigger thresholds & other searches

Optimum Trigger: what has been achieved in CUORE-0

Obtained trigger thresholds range from 4 keV up to 12 keV

Signals Noise

Signal/Noise shape discriminator: 𝜓D of triggered filtered pulses w.r.t. ideal one

CUORE0 CUORE0

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SLIDE 18

CUORE

Conclusions

  • Best limit on 0v DBD half-life of 130Te;

ü first CUORE result published in PRL;

  • Technological achievements:

ü first ton scale bolometric detector in

  • peration;

ü largest and most powerful dilution refrigerator in operation; ü developed new methods to reduce noise and set best working conditions for the detector;

  • Work in progress:

v after acquiring the first two datasets for physics, a new optimization phase started; v resumed data-taking in May 2018; v exploring the possibility to lower the trigger thresholds to perform DM searches;

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SLIDE 19

CUORE

List of references

  • CUORE Collaboration, First Results from CUORE: A Search for Lepton Number Violation via 0𝜉𝛾𝛾

Decay of 130Te, Phys. Rev. Lett. 120, 132501 (2018);

  • A. D'Addabbo, C. Bucci, L. Canonica, S. Di Domizio, P. Gorla, L. Marini, A. Nucciotti, I. Nutini, C.

Rusconi, B. Welliver, An active noise cancellation technique for the CUORE Pulse Tube Cryocoolers, arXiv:1712.02753 [physics.ins-det];

  • CUORE Collaboration, Low Energy Analysis Techniques for CUORE. European Physical Journal C 77,

857 (2017);

  • Sergio Di Domizio, Filippo Orio, Marco Vignati, Lowering the energy threshold of large-mass

bolometric detectors, JINST 6 (2011) P02007;

  • S. Dell’Oro, Optimization of the CUORE detector during the commissioning phase, Ph.D. thesis, Gran

Sasso Science Institute (2017);

  • L. Marini, The CUORE experiment: from the commissioning to the first 0𝜉𝛾𝛾 limit, Ph.D. thesis,

Università degli Studi di Genova (2018);

  • A. Branca - PM2018

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SLIDE 20

CUORE

Additional material

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SLIDE 21

CUORE

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

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

Bolometric technique: 130Te

Bolometric detectors: detector also the source of 0ν DBD:

  • high efficiency;
  • excellent energy resolution;
  • large masses are achievable;

130Te: a good candidate source for

0vDBD:

  • high natural isotopic abundance;
  • Q-value (2528 keV) above most of

the natural radioactivity;

  • nuclear matrix elements and phase

space on average;

Running period

1990 1995 2000 2005 2010 2015 2020 2025

t0ν

1 /2

[yr]

(90% C. L.) 1019 1020 1021 1022 1023 1024 1025 1026

6 g 21 g 34 g 73 g 334 g 4 crystal array MiDBD Cuoricino CUORE-0 CUORE

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SLIDE 22

CUORE

Last phases of CUORE installation

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

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SLIDE 23

CUORE

Suspension system

Abatement of vibrations: mechanical decoupling from the outside environment:

  • detector

suspension independent from that

  • f

cryogenic and calibration systems:

  • 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);

Reduction of radioactive background (from outside):

  • outer neutron shield: polyethylene + borated powder;
  • outer gamma shield: lead shield;

Y-Beam Minus-K Elastometers

External lead shield (~70 t)

H3BO3 panels Polyethylene MSP

  • A. Branca - PM2018

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SLIDE 24

CUORE

Calibration system

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:

  • 232Th γ-ray sources every ~month (239 keV to 2615 keV);
  • sources are outside cryostat during physics data-taking and

lowered into cryostat and cooled to 10 mK for calibration;

  • sources are put on strings, lowered under their own weight;
  • a series of tubes in the cryostat guides the strings;
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SLIDE 25

CUORE

Crystals production and copper cleaning

Production of the TeO2 crystals:

  • by Shanghai Institute of Ceramics,

Chinese Academy

  • f

Science (SICCAS);

  • all
  • perations

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

  • f

a thin layer

  • f

material (from 1 μm to 100 μm);

  • A. Branca - PM2018

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SLIDE 26

CUORE

Roman Lead

  • 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);

  • A. Branca - PM2018

26

Normally Pb contains

210Pb

with 10-1000 Bq/kg (half life ~ 22 y)

210Pb in roman

Pb < 4 mBq/kg

30 May 2018

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SLIDE 27

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

expected dominant contribution 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

30 May 2018

slide-28
SLIDE 28

CUORE

Physics spectrum compared to CUORE-0 (𝛿 region)

13 December 2017

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slide-29
SLIDE 29

CUORE

30 May 2018

  • A. Branca - PM2018

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β/γ dominated α dominated

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

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;
slide-30
SLIDE 30

CUORE

Effective Majorana mass limit

Interpreting the combined half-life limit as a limit on the effective Majorana neutrino mass:

  • framework of models where the 0v DBD is mediated by an exchange of a light Majorana neutrino;

(T 0ν

1/2)1 = G0ν(Q, Z) |M 0ν|2 |hmββi|2

m2

e

Combined 90% limit:

𝑛vv < 110 − 520 𝑛𝑓𝑊 (𝑓𝑦𝑞𝑝𝑡𝑣𝑠𝑓: 86.3 𝑙𝑕 M 𝑧𝑠)

Half-life limits:

  • 130Te: 1.5 × 1025 yr from this analysis PRL 120, 132501 (2018)
  • 76Ge: 8.0 × 1025 yr from PRL 120, 132503 (2018)
  • 136Xe: 1.1 × 1026 yr from Phys. Rev. Lett. 117, 082503 (2016)
  • 100Mo: 1.1 × 1024 yr from Phys. Rev. D 89, 111101 (2014)

Nuclear Matrix elements from:

  • JHEP02 (2013) 025
  • Nucl. Phys. A 818, 139 (2009)
  • Phys. Rev. C 87, 045501 (2013)
  • Phys. Rev. C 87, 064302 (2014)
  • Phys. Rev. C 91, 034304 (2015)
  • Phys. Rev. C 91, 024613 (2015)
  • Phys. Rev. C 91, 024309 (2015)
  • Phys. Rev. Lett. 105, 252503 (2010)
  • Phys. Rev. Lett. 111, 142501 (2013)

𝑕„ ≅ 1.27

13 December 2017

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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 limit (Te), PRL 2018 Cuoricino + CUORE-0 CUORE sensitivity (Te) Normal hierarchy Inverted hierarchy

1 1 10 2 10 3 10

Other isotopes Mo Ge Xe