The SABRE Proof of Principle Simone Copello on behalf of the SABRE - PowerPoint PPT Presentation

The SABRE Proof of Principle Simone Copello on behalf of the SABRE collaboration *Gran Sasso Science Institute, L’Aquila, Italy TAUP 2019 - 8/14 September, Toyama, Japan 1

Outline Experimental goal and strategies ● Annual modulation signature in DAMA ○ SABRE key features ○ SABRE Proof of Principle (PoP) ● PoP and Full Scale Experiment ○ PoP status ○ NaI-33 crystal ● Alpha rate ○ Conclusions ● Simone Copello - TAUP 2019, September 9th - Toyama, Japan 2

Annual modulation signature Single-site nuclear recols are considered for DM direct detection. Annual modulation of event rate is a powerful signature caused by the combination of Earth and Sun velocities within the dark matter halo. Expected event rate is 10 -1 to 10 -6 events/day/kg A signal has been observed by the DAMA/LIBRA experiment at LNGS, Italy. Ingredients for the annual modulation: From arXiv:1805.10486 ● Standard halo model: spherical halo surrounding the galaxy, with a local mass density of ~0.3 GeV/c 2 /cm 3 DAMA/LIBRA–phase2 ● WIMP velocity (with respect Exposure : 1.13 ton × year (6 years) to Earth): Sensitive mass : about 250 kg of radio-pure NaI(Tl) crystals Statistical significance : 9.5 σ in (1 - 6) keV, 12.9 σ in (2 - 6) keV* [220 + 15 cos ω(t-t0)] km/s * Including DAMA/NaI and DAMA/LIBRA–phase1 data Simone Copello - TAUP 2019, September 9th - Toyama, Japan 3

S odium iodide with A ctive B ackground RE jection SABRE aims to detect the annual modulation signal by using NaI(Tl) crystals, in order to have a direct (model independent) confirmation/confutation of DAMA results. 4 key features: 1. Active background rejection: active veto of liquid scintillator 2. Low energy threshold: High QE Hamamatsu PMTs, directly coupled to the crystals 3. Double location: both in Northern and Southern hemispheres 4. High purity crystals: High purity powder and clean crystal growth method More detail about the SABRE project can be found the paper “The SABRE project and the SABRE Proof-of-Principle” https://link.springer.com/article/10.1140/epjc/s10052-019-6860-y (arXiv:1806.09340) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 4

SABRE collaboration ~50 physicists from three countries Australia ● Australian Nuclear Science and Technology Organization ● Australian National University ● Swinburne University of Technology ● University of Adelaide U.S.A ● University of Melbourne ● Princeton University ● Lawrence Livermore National Laboratory Italy (LLNL) ● Laboratori Nazionali del Gran ● Pacific Northwest Sasso (LNGS) National Laboratory ● University of Milano and INFN (PNNL) ● University of Roma Sapienza and INFN ● Gran Sasso Science Institute Simone Copello - TAUP 2019, September 9th - Toyama, Japan 5

1. Active veto Intrinsic and environmental backgrounds are reduced by means of material selection, underground labs and shielding. 40 K represents a consistent fraction of the background in the ROI but can be tagged, as well as 22 Na. 40 K background with active veto: Rejection efficiency ~85% Picture from paper on the SABRE PoP Monte Other intrinsic background sources, that cannot be tagged by Carlo simulations: https://www.sciencedirect.com/science/article/ the veto, are 87 Rb, 232 Th (chain), 238 U (chain) and 3 H pii/S0927650518301804?via%3Dihub Simone Copello - TAUP 2019, September 9th - Toyama, Japan 6

2. Low energy threshold Modulation amplitude, in general, is larger at smaller energies. Light production : High crystal light yield Light collection : Hamatsu R11065 3” PMTs ● 2 PMT per crystal: coincidence trigger ● PMTs directly coupled to the crystal: no light guides ● High quantum efficiency (~35%) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 7

3. Double location Seasonal effects have opposite phases in the opposite hemispheres. SABRE North at Laboratori Nazionali del Gran Sasso (LNGS), Italy SABRE South at Stawell Underground Physics Laboratory (SUPL), Australia Simone Copello - TAUP 2019, September 9th - Toyama, Japan 8

4. High purity crystals Residual impurities in the crystal are predominant source of background, once reduced the environmental radioactivity, for DM search. Effort of Princeton University with some Industrial Partners: ● Production of Ultra-high purity powder: Astrograde powder (PU & Sigma Aldrich – now Merck) ● Powder handling and treatment methods ● Crucible selection, cleaning and treatment ● Crystal growth using vertical Bridgman technique in a sealed ampoule (PU & RMD) ● Crystal cutting, polishing and handling ● Development of high sensitivity ICP-MS measurements 2kg test crystal Example of a good growth of a 2 kg crystal obtained in 2015. 40 K content was 9 ppb from ICP-MS (the same content of the Astro-Grade powder) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 9

SABRE Phase I - Proof of Principle Setup ready at LNGS Goals: ● Fully characterise SABRE NaI(Tl) intrinsic and cosmogenic backgrounds ● Test few (≈ 3) crystals ● Test active veto performance veto Layout: ● 1 NaI(Tl) crystal module per time (“dry” insertion) ● Crystal mounted inside a Cu enclosure and directly coupled to 2 PMTs Hamamatsu ULB R11065-20 3” PMTs, High QE ● Active veto: 2 t PC+PPO (3g/l) scintillator (from Borexino exp) read by 10 Hamamatsu R5912-100 PMTs ● External passive shielding (lead, polyethylene and water) purged with gas nitrogen ● Material selection (using ICP-MS and HPGe) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 10

SABRE Phase II: Full Scale Experiment Twin detectors SABRE North at LNGS and SABRE South at SUPL Goals: ● Lowest background NaI experiment for Dark Matter search ● Confirm/Reject annual modulation with amplitude observed by DAMA/LIBRA with 3 years of data Layout: ● > 50 kg of NaI(Tl) crystal, active veto, external shielding, double location ● Final design and schedule depends on the outcome of PoP DAMA/LIBRA FACTS ● NaI(Tl) crystal detector mass 250 kg SABRE GOALS nat K ● ≈13 ppb nat K ● ≤ 10 ppb ● Rb < 0.35 ppb ● Rb ≤ 0.1 ppb ● Th ≈ 0.5 – 7.5 ppt ● U/Th < 1ppt ● U ≈ 0.7 – 10 ppt low 3 H and 210 Pb contamination ● 210 Pb ● 10-30 µBq/kg ● LY > 10 pe/keV ● LY 6-10 pe/keV ● Rate in the ROI (2-6 keV) < 1 cpd/keV/kg ● Threshold 1 keV ● Rate in the ROI (2-6 keV) 1 cpd/keV/kg (single hit) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 11

Proof of Principle status The veto vessel, cleaned and internally covered with Lumirror reflector, is in its final position. All the veto PMT have been tested. The copper tube will host the crystal enclosure . This solution avoids contact of liquid scintillator with air: safe and practical way to mount/change crystal in PoP set-up. Simone Copello - TAUP 2019, September 9th - Toyama, Japan 12

Proof of Principle status Crystal Insertion System A frame is mounted on a steel plate above the vessel. A motorized pulley connected to an alignment system, guides the enclosure into the copper tube . The enclosure is connected to a flange via a steel bar. Enclosure mock-up Simone Copello - TAUP 2019, September 9th - Toyama, Japan 13

Proof of Principle status Shielding ● Water tanks ( ≥ 80 cm top and side) ● High density Polyethylene (10 cm top and bottom, ≥ 40 cm side) ● Lead basement (15 cm) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 14

Proof of Principle status All the needed infrastructures are completed: ● Fluid Handling ● Safety plant ● Slow control system ● Power (normal + UPS power) ● Network ● Control room (DAQ, High voltage...) PoP is ready to be filled with liquid scintillator but we still waiting for the approval from the laboratory. Simone Copello - TAUP 2019, September 9th - Toyama, Japan 15

Passive shielding setup at LNGS Small underground shielding used for preliminary crystal measurements, it can host two crystal enclosures. Same DAQ and reconstruction software of PoP. Enclosed into a Radon box. 5/10 cm of copper + ≥ 15 cm of lead. NaI-33 data have been collected here (next slides) Simone Copello - TAUP 2019, September 9th - Toyama, Japan 16

NaI-33 crystal Underground at LNGS ● Astrograde powder by Sigma Aldrich and crucible prepared at PU. ● Ready October 2018 - Assembled in mid-May 2019 . ● Potassium measurement via ICP-MS: ~ 4 ppb ● Mass ~ 3.5 kg after cut and polishing ● Arrived at LNGS on August 6, 2019 (by boat to reduce cosmogenic activation). Final crystal portion K content: fit from three samples taken near tip, tail and far-end tail measured by ICP-MS (at Seastar). Simone Copello - TAUP 2019, September 9th - Toyama, Japan 17

NOTE: all the plots and numbers reported in this NaI-33: LY and resolution slide must be considered preliminary results Currently the spectrum is still dominated by cosmogenic isotopes decays. 241 Am source used to measure energy resolution and light yield (LY) on the 59.5 keV line: • Peak at (12.17 ± 0.01) nVs Light Yield FWHM/E • σ = (0.62 ± 0.01) nVs 11 phe/keV 12.3% Preliminary For comparison… ● DAMA/LIBRA phase-2: 15.8% @59.5 keV ● ANAIS-112: 11.2% @59.5 keV ● COSINE-100: 11.8% @59.5 keV Simone Copello - TAUP 2019, September 9th - Toyama, Japan 18