CUORE: the first bolometric experiment at the ton scale for CUORE - PowerPoint PPT Presentation

CUORE: the first bolometric experiment at the ton scale for CUORE rare decay searches Antonio Branca – DFA Università degli Studi di Padova & INFN Sezione di Padova On behalf of the CUORE Collaboration PM2018 – 14 th Pisa Meeting on Advanced Detectors, 30 May 2018

The signal CUORE is searching for CUORE To build a high sensitivity experiment: Energy spectrum of the two electrons in the final state sens . ∝ i . a . ⋅ ε ⋅ M ⋅ t ( ) 0 ν T 1/2 Δ E ⋅ B • 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; 30 May 2018 A. Branca - PM2018 2

Bolometric technique in CUORE CUORE A (A) Copper frame: 10 mK heat sink (B) PTFE holders: D weak thermal coupling Radiation: C energy deposit (D) Si joule heater: B E reference pulses (C) TeO 2 crystal: energy absorber (E) NTD Ge thermistor: resistive thermometer Amplitude (a. u.) E 1 high efficiency; Δ T = • C ( T ) 0.8 excellent energy resolution; • Readout Δ T 3 0.6 ⎛ ⎞ large masses achievable; T • C ( T ) = ⎜ ⎟ ϑ D 0.4 ⎝ ⎠ 130 Te high natural isotopic • Low temperature needed: @𝑼 = 𝟐𝟏 𝒏𝑳 abundance; 0.2 𝐷~10 67 𝐾 𝐿 ; ∆𝑈 = 0.1 𝑛𝐿 130 Te Q-value 2528 keV; • 0 𝑁𝑓𝑊 ; 𝜐~1𝑡 0 2 4 6 8 10 Time (s) 30 May 2018 A. Branca - PM2018 3

A rare event search CUORE Searching for a rare event (0ν DBD): 𝜐 > 10 DE6DF 𝑧𝑠 ……………………… Extremely important to reduce as much as possible backgrounds: a. natural radioactivity from outside the detector: CUORE installed @ LNGS underground REDUCTION • cosmic ray muons induced background; laboratories (~3600 m.w.e.) • neutron and gamma fluxes; • Strict protocols for crystal b. natural radioactivity from the detector itself: production @ SICCAS; • long-lived nuclei ( 40 K, 238 U, 232 Th); • Cleaning techniques developed @ REDUCTION • anthropogenic radioactive LNL for copper parts near crystals; isotopes ( 60 Co, 137 Cs, 134 Cs); • Strict protocol for assembling and • cosmogenic radioactive isotopes ( 60 Co); installation; c. mechanical vibration noise: Suspension/damping systems and REDUCTION new noise cancellation tools • cryogenic system and seismic noise; 30 May 2018 A. Branca - PM2018 4

Cryogenic system CUORE 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 ( 4 He 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 μ W @ 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); 30 May 2018 A. Branca - PM2018 5

Cryostat commissioning CUORE Commissioning completed in March 2016 : 300 K stable base T = 6.3 mK over 70 days (no detector, full load); • 40 K full detector read-out chain (electronics, DAQ) test, • temperature stability with Mini-Tower (8 crystal tower); 4 K successful deployment of the calibration sources at base • temperature; 600 mK System ready for detector installation. 50 mK No noise 10 mK optimization 30 May 2018 A. Branca - PM2018 6

Detector assembling and installation CUORE Strict protocol adopted for each step of assembling/installation (developed and tested in predecessor experiment CUORE0): Assembling : in N 2 atmosphere and within glove Installation : protected area inside clean room boxes to avoid radioactive recontamination flushed with radon free air; protective bags flushed (between 2013 and 2014); with N 2 for overnight and emergency storage (started after cryostat commissioning); 5. towers installation 2. tower assembly 1. sensors gluing 3. wire bonding 4. towers storage 30 May 2018 A. Branca - PM2018 7

The CUORE “core” installed CUORE Design specifics: • detector arrangement: 19 towers with 13 floors of 4 crystals each; • crystals: 988 crystals, 5 cm 3 , 750 g each; • total TeO 2 mass of 742 kg; • total 130 Te 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 10 6D 𝑑/(𝑙𝑓𝑊 M 𝑙𝑕 M 𝑧𝑠) ; • energy resolution: 5 𝑙𝑓𝑊 𝐺𝑋𝐼𝑁 in the Region Of Interest (ROI); • All 19 towers installed UV = 9 M 10 DX 𝑧𝑠 (5 years, 90% C.L.); between July-August 2016 0v-DBD projected sensitivity: 𝑈 • T/D 30 May 2018 A. Branca - PM2018 8

Detector cool down CUORE After towers installation, the cryostat was closed between September-November 2016: After the cooldown started an cooldown started on Dec 5, 2016: lasted ~26 days (without • important phase of detector counting technical stops for system debugging); optimization alternated to data- on Jan 26, 2017 reached a stable base temperature of T = 7 mK; • taking periods Last 4 days of cooldown: DU switched on Diode thermometer at 10mK plate cryogenics 10 debugging 2 10 electronics 1 Still plate noise studies T [K] T (K) HEX plate 0.1 MC plate 10 CUORE cool down Start: 2017-01-23 10:00 0 . 01 0 0.5 1 1.5 2 2.5 3 3.5 4 12/05-12:16 12/22-14:10 01/08-16:04 01/25-17:59 Time ∆ t [d] 30 May 2018 A. Branca - PM2018 9

Setting the best working temperature CUORE 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; FWHM vs Temperature - Tl (2615 keV) and Ac (911 keV) peaks - October 2017 Temperature Scan CUORE Preliminary CUORE Preliminary 12 Baseline and Resolutions 10 Pulser on physics 8 FWHM (keV) resolutions events (from 6 (from July September 2017 scan) 2017 scan) 4 2 FWHM Tl 2615 keV FWHM AC 911 keV 0 11 12 13 14 15 16 17 18 19 Temperature (mK) 30 May 2018 A. Branca - PM2018 10

Minimization of vibrational noise CUORE Developed tool to minimize vibrational noise from PTs: 10 mK temperature: use linear drives (LD) to control PTs’ rotating valves; • before and after LD PTs phase scan to find the configuration of minimum • switch on noise across the whole detector; PT induced noise on each channel vs PTs phase configuration ph 1 Median Normalised Noise A median overall channels vs PTs phase configuration − 1 10 0 1000 2000 3000 4000 5000 PhaseID 30 May 2018 A. Branca - PM2018 11

Maximize SNR CUORE 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; • Example of I-V (Load-Curve) for a channel Reference pulses for different amplitudes @ 𝐽 [\]^ Amplitude (a. u.) AP with pulser amplitude at 2200 1 AP with pulser amplitude at 1800 AP with pulser amplitude at 1200 0.8 AP with pulser amplitude at 500 CUORE Preliminary 0.6 0.4 CUORE Preliminary 0.2 0 0 1 2 3 4 5 Time (s) 30 May 2018 A. Branca - PM2018 12

Data taking for physics analysis CUORE Detector optimization ended in April 2017 to start science runs: • Dataset 1 : 3 weeks of data bracketed by 2 calibration periods (May - June 2017). TeO 2 exposure 37.6 𝑙𝑕 M 𝑧𝑠 ; still room for performance improvements; Ø Detector optimization restarted in July 2017: careful investigation/upgrades to the electronics ü grounding in the CUORE Faraday cage; Dataset 1 Introduced PTs phase scans to refine the abatement ü Dataset 2 of induced noise; optimization of the operating temperature and ü detector working points; software and analysis upgrades; ü After the second optimization phase, resumed data-taking: Improved resolution between the two datasets Dataset 2 : same procedure as first dataset (August – • September 2017). TeO 2 exposure 48.7 𝑙𝑕 M 𝑧𝑠 ; 30 May 2018 A. Branca - PM2018 13