Results of direct dark matter detection with CDEX experiment at CJPL - PowerPoint PPT Presentation

Results of direct dark matter detection with CDEX experiment at CJPL Hao Ma ( 馬豪 ) for the CDEX Collaboration Tsinghua University XVI International Conference on Topics in Astroparticle and Underground Physics 9-13 Sept. 2019, Toyama, Japan

OUTLINE • Introduction to CDEX and CJPL • Recent DM results from CDEX experiment • Technical R&D and Future plan • Summary 2

CDEX Collaboration • China Dark Matter EXperiment  Formed in 2009, 11 institutions and ~70 people;  Searching for light DM by P-type Point-Contact Germanium detectors 3

CDEX Experiment • DM detection w/ Ge prepared since 2003 and started in 2005 in Y2L (5g); • CDEX-1: Development of PPC Ge detector, bkg understanding, since 2011; • CDEX-10: Performances of Ge array detector immersed in LN 2 , since 2016; • CDEX-10X: Home-made Ge detector and Ge crystal growth; Ionization signal by Nuclear recoil 4

China Jinping Underground Laboratory • World’s deepest underground lab, CJPL • Near Xichang city, Sichuan Province, Southwest China • Constructed by Tsinghua U. and Yalong Hydropower Company in 2009-2010 • Two DM exp. (CDEX, PandaX) + LBF( radio-assay) operated now • Extension project, CJPL-II, final exam and expected to be completed in 2022 Cheng et al., Annu. Rev. Nucl. Part. Sci. 2017. 67:231 5

CDEX-1 Status • 2 sub-stages: CDEX-1A(prototype, 2011)  1B(upgraded, 2013); • Single-element ~1kg PPC Ge detector w/ cold finger; • Low-bkg Pb&Cu passive shield + NaI veto detector; • Located in PE room at CJPL-I; Testing CDEX- tank 10 CDEX- 1A CDEX- 1B 6 CDEX-1 inside PE room CDEX-1A&B: 1kg PPC Ge × 2 Layout of PE room, CJPL-I

CDEX-1B Results • Detector upgraded w/ lower JEFT noise and material bkg; • >4 years run (Run-1&Run-2), >1200 kg·day exposure; • Achieving 160 eVee energy threshold; • Sensitivity improved and extending to 2 GeV/c 2 . Run-1 Time-integrated (TI) analysis: CPC 42, 023002, 2018 CDEX-1B SI SD 7

Annual Modulation analysis from CDEX-1B • Maximum χ -N rates in June due to Earth’s motion relative to the galactic DM halo  Annual modulation effect • AM analysis on CDEX1B data of >4 years Run-1 (751.3 days) Run-2 (428.1 days) 8

CDEX-1B AM analysis (new) Bulk event count rates vs. time (after B/S cut) • Count rates vs. time Compton contribution from High-energy gammas arXiv: 1904.12889 9

CDEX-1B AM analysis Best- fi t of modulation amplitude w/ phase=152.5day <standard halo> SI Limits at 90% C.L. from AM v 0 = 220 km/s, ρ DM = 0.3 GeV/cm 3 , arXiv: 1904.12889 v esc = 540 km/s fp/fn=1  CDEX-1B excludes DAMA/LIBRA phase-1’s interpretation CDMS-II, 1203.1309. CoGeNT, 1401.3295. with the spin-independent WIMP interaction with Standard DAMA/LIBRA, JCAP04, 010(2009); EPJC 67, 39 (2010) / 73, 2648 (2013). Halo model in Germanium crystal. 10 XMASS-1, 1808.06177.

Sub-GeV WIMPs: Migdal effect analysis (new) • Time-Integrated Analysis with Migdal: 737.1 kg·d, Migdal effect (M. Ibe et al.,2018) w/ Eth 160 eVee; • AM Analysis: 1107.5 kg·d, w/ Eth 250 eVee; • Leading sensitivity in m DM ~ 50-180 MeV/c 2 ; Expected measureable spectra SI, 90% C.L. upper limits AM, 90% C.L. upper limits arXiv: 1905.00354 11

CDEX-10 Status • Array detectors: 3 strings with 3 detectors each, ~10kg total; • Direct immersion in LN 2 ; • Prototype system for future hundred-kg to ton scale experiment • Light/radio-purer LN 2 replacing heavy shield i.e. Pb/Cu; • Arraying technology to scalable capability; CDEX-10: ~10kg PPC Ge array 12

First Result of CDEX-10 • First results from 102.8 kg·day exposure w/ Eth 160eV; • Bkg level: ~2 cpkkd @ 2-4 keV; • More stringent SI limits on 4-5 GeV/c 2 ; PRL120, 241301, 2018 CDEX-10 13

First Result of CDEX-10 • First results from 102.8 kg·day exposure w/ Eth 160eV; • Bkg level: ~2 cpkkd @ 2-4 keV; • More stringent SI limit on 4-5 GeV/c 2 ; • Ultra-fast events observed in bulk  backgrounds from p+ face; PRL120, 241301, 2018 Sci. China-Phys. Mech. Astron. 62, 031012 (2019 ) 14

Technical R&D: Ge detector fabrication • CDEX10+X home-made Ge detectors; • Understand & reduce detector intrinsic bkg; • Various types, ~20 detectors • P-type planar/coaxial; • P-type point contact/ BEGe; good performance keeping, >1400 days • Long time stability 1400 days  Commercial Ge crystal;  Structure machining; Assembly & testing lab  Li-drift and B-implanted;  Home-made ULB PreAmp;  Underground EF-Cu;  Underground assemble;  Underground testing… 15 Vacuum systems

Technical R&D: Ge detector fabrication • Commercial Ge crystal + stainless steel canister; • T1 detector: 500g Ge(φ50 × 50mm) + CMOS ASIC preAmp; • Works w/ expected performance! • Going on to improve bkg, low-noise electronics… 201712 T1 (3.15d) 201809 T1 (8.83d) Co-57 spectrum threshold ~300eV Ge-68 KX Background spectrum @CJPL FWHM=0.48keV@122keV_Co57 Tested in CJPL-I 16

Technical R&D: Ge detector fabrication • Vacuum chamber, structure materials, not conducive to further reduce the radioactive background; • ASIC-based preamplifiers work well in liquid nitrogen;  Develop bare HPGe detector immersed into LN 2 !  Immerse the detector into LN 2 for ~8 hours, we got a stable leakage current ~10 pA for 1000V bias voltage. 30 25 Leakage Current (pA) LN2 20 15 10 5 0 0 2 4 6 8 Bare HPGe detector Bare HPGe in LN 2 Time (h) 17 PPC: φ 50mm x 50mm, Depleted voltage: ~800V

Technical R&D: CMOS ASIC Front-end Electronics • Light DM search  low noise/threshold (low capacity, etc) • Very close to Ge crystal  low bkg (radiopure, low-mass, etc) • ASIC preamplifier @ 77K • PCB material: PTFE (Rogers 4850); • ENC ~26e(<200eV) w/ 4μs shaping time, mainly from 1/f noise (~21e ); Details in JINST (2018) 13: 8019 Noise components analysis 18

Technical R&D: UG E-forming copper and Assay • Prototype setup for underground EF-Cu production • Cathode mandrel: 316L stainless steel, φ90x380mm ; • Plating bath: PE, φ400x500mm; • Goal: Majorana copper, U/Th content ~ O(0.1μBq/kg); • Test run in Tsinghua U. and moved to CJPL-I; • U/Th Analysis by ICP-MS • Wet chemistry procedure, blank sensitivity ~10 -13 g/g UG copper e-forming facility@CJPL-I before 19 optimized electrical parameters ICP-MS E-forming prototype

Future Plan - Detectors • Customized detectors by commercial companies • 2kg arrived, another 5kg ordered from ORTEC; • Particular control of detector fabrication process above ground; • Home-made detectors • Improve T1 w/ low bkg material and low noise electronics; • Set up underground fabrication and testing facility @CJPL-II; Detector production: 45days + Ground transportation: 60 days + Underground cooling: 180days Cosmogenic bkg: 0.03cpkkd(sim.) 20

Future Plan – New location • CJPL-I to CJPL-II See talk by Q. Yue, UL#2, Monday • Volume: 4000 m 3 to 300,000 m 3 ; • 1 main hall (6.5x6.5x42m) to 8 main halls (14x14x60m each); • Additional pit for next-generation CDEX; Entry Exit Layout of CJPL-II CDEX here  21

Future Plan - Experiment • CDEX10X moving to a 1725m 3 LN 2 tank (φ13x13m) located in the pit; • Construction of LN 2 tank kicked off in Nov. 2018 and done end of 2019; • CDEX-100 under technical design. Cooling and shielding CDEX Pit (top view) 22

Future Plan - Setup • CDEX10X moving to a 1725m 3 LN 2 tank (φ13x13m) located in the pit; • Construction of LN 2 tank kicked off in Nov. 2018 and done end of 2019; • CDEX-100 under technical design. Cooling and shielding CDEX Pit (top view) 23

Future Plan – Main Goals • 0νββ (Under LEGEND) • DM • Taking advantages of Ge detectors; • WIMPs; • Combined with Legend-1T • Axion, Dark Photon… • Location Undetermined! ββ(2 v) as a background 24 Assuming

CDEX Roadmap CDEX-1A/B CDEX-10 CDEX-100 / CDEX-1T CJPL-II CJPL-I 2011 2016 202X  PPC Ge detector with a mass  10 kg PPC Ge detector  Ge array in large-volume LN 2 of up to ~1 kg array immersed into LN 2  multi-purpose: DM and 0νββ(LEGEND)  PRD88, 052004, 2013  PRL120, 241301, 2018 Key technologies:  PRD90, 032003, 2014  Ge crystal growth and 76 Ge enrichment  PRD90, 091701, 2014  Ge detector fabrication Lower background  PRD93, 092003, 2016  Ultra-low background VFE Lower threshold  PRD95, 052006, 2017 ( Axion )  Ultra-pure copper for structure and cables  Sci. China (2017) (0νββ)  Natural Ge detectors as veto 25  CPC42, 023002, 2018  ……

Summary • CDEX: unique advantages of PPC Ge detectors for light DM search at CJPL • New AM limits from >4-year data ruled out DAMA/LIBRA phase1 and CoGeNT results, best sensitivity below 6 GeV/c 2 • New Migdal effect analysis: leading sensitivity at m DM of 50-180MeV/c 2 • New site for next-generation CDEX in Hall C1 of CJPL-II project • Easy scalability and lower bkg expected w/ new large cryo-tank; • Ongoing efforts on home-made Ge detector, FE electronics, crystal growth, UG copper e-forming … • Other physics: Axion, dark photon, 0νββ(LEGEND), … 26 Hao MA, Tsinghua U., mahao@tsinghua.edu.cn

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Energy resolution of detectors C1A C1B C10B 28

Background stability of AM • Decay with time as expected 1.1-1.2keV Cosmogenic L-Shell X-ray contribution (blue points) 29