DAMIC at SNOLAB Alvaro E Chavarria University of Chicago for the DAMIC Collaboration 1
Outline • Charge coupled devices (CCDs) as detectors for low-energy particles. • Characterization of the DAMIC devices. • DAMIC installation at SNOLAB. • Low-mass dark matter search results. • Background suppression techniques. • Future of the DAMIC program. 2
Charge coupled device σ xy σ xy ~ z y Pixel array x z y x x Free 675 µm charge ± carriers Ionizing Device is “exposed,” collecting charge particle z until user commands readout. Fully depleted substrate Readout can be slow / non-destructive : very low noise (few e - ). Silicon band-gap: 1.2 eV. 15 µm Mean energy for 1 e-h pair: 3.8 eV. 3
Particle tracks 6 keV front X-ray? n, WIMP? Diffusion e limited 50 pixels Back α 6 keV back μ DAMIC CCD: 15x15 µm 2 pixels Front 2080 4180 4190 4200 4210 4220 1000 1 2000 3000 2 4000 5000 3 6000 7000 4 8000 9000 5 10000 5 10 15 20 25 30 5 10 15 20 25 30 Energy measured by pixel / keV Energy measured by pixel / keV 4
Device performance 5 Linearity demonstrated for signals <10 e - . 10 Image Blank Gaussian fit 1.08 ) 4 10 ee X-rays mean = -0.003 0.001 k(E) / k(5.9 keV � 1.06 Entries per bin Optical photons = 1.827 0.001 � � 1.04 3 10 1.02 1 2 10 White readout noise 0.98 0.96 10 <2 e - RMS ~ 7 eV ee 1 − 10 1 10 Ionization signal [keV ] ee 1 �� ��������� ��� � Characterization of Compton � 10 0 10 20 30 40 - Pixel Value [e ] ��� background at low energies �������� �� �� � � � ���� ������� ������������� ���� ���������� ������ �� ������ ���� ��� � � � ����� ���� Si K-shell ���� ���� ���� ���� Si L-shell ���� ���� ���� ���� ��� ��� arXiv:1706.06053 ��� ���� ��� ���� ��� ���� ��� ���� ��� � ��� � ��� � ��� � ��� � � ����� 5
Nuclear recoil response a) Cross-section of setup b) 124 Sb- 9 Be source detail 3 He counter 24 keV Vacuum chamber 2.75 cm BeO cap neutrons Source BeO cylinder from 20 cm Activated CCD 9 Be( γ ,n) Lead shielding antimony rod reaction BeO base Table Table 10 Dougherty (1992) ] 1000 -1 Data - full BeO ) Gerbier et al. (1990) ee Number of nuclear recoils [(10 eV Zecher et al. (1990) Best-fit with Monte Carlo spectrum 124 9 Sb- Be (2016) 800 Antonella (2017) Lindhard, k=0.15 Single-recoil spectrum ] 2 � / ndf 142 / 154 ee 600 1 Prob 0.74 [keV very similar to signal -1 f (0.06) 0.63 0.01 � PRD94 082007 from 3 GeV WIMP. -1 f (0.3) 1.94 0.02 � JINST12 P06014 400 e f(3.2) End-point = 3.2 keV r 0.61 0.02 � E y offset 1.4 � 1.0 Calibration down 200 to 60 eV ee . 1 − 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 10 E [keV ] E [keV ] e r ee nr 6
2 km underground 7
SNOLAB Installation 5.8 g 16 Mpix CCD Poly- 6 cm VIB ethylene Lead Kapton Copper Lead block Kapton signal cable module signal cable Cu box with CCDs J. Zhou Cu vacuum vessel 8
WIMP search Elastic scattering of WIMPs with silicon nuclei. Recoil spectrum 2D Gaussian in Si target distribution of free charge on pixel array. 2 All data 1 × 1 1 × 100 Surface (sim) 1.8 candidates 1.6 1.4 1.2 σ xy [pix] 1 0.8 0.6 0.4 Measure E and σ xy 0.2 for every event. 0 0 1 2 3 4 5 6 7 8 9 10 0 4 8 12 16 E [keV ee ] Entries 9
WIMP search 0.6 kg days of data with test devices 0.9 0.8 at SNOLAB. 0.7 Detection efficiency ~ 30 dru total background. 0.6 -36 10 0.5 WIMP-nucleon cross-section [cm ] This work 2 PRD94 082006 0.6 kg d -37 0.4 10 Signal (1 × 1) 0.3 Signal (1 × 100) -38 10 0.2 Background (1 × 1) Background (1 × 100) 0.1 -39 10 CRESST II 2015 - 52 kg d 0 DAMA/Na 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 E [keV ] -40 ee 10 Observed spectrum in fiducial region CDMSLite - 70 kg d -41 10 3 -42 10 2.5 LUX - 14 ton d CDMS-II Si - 140 kg d ee Events per 100 eV -43 2 10 1 10 -2 WIMP Mass [GeV c ] 1.5 Spectrum consistent with Compton 1 scattered electrons in fiducial region: 0.5 No WIMP signal. 0 0 1 2 3 4 5 6 7 E [keV ] 10 ee
Hidden photon search ~1 week of data with 1 CCD. Absorption Leakage current 4 e - mm -2 d -1 . Si bulk of hidden- �� � �� 675 µm photon - e - - - Ionization PRL118 141803 - dark �� � �� matter. �� � �� Hidden Photon �� � �� � �� � ������� ������� � ����� ����� �� � �� ����� ���� �� � ���� ��� � � ����� ���� ������� ���� � ��� � � � � � � � ������ �� ������ ������� ���� �� � �� �� � ��� � � ����� ������� ������� � ��� � � � � � � � ����� ����� ���� ���������� �� � �� �� � �� � �� � � � ���� � � � �� � Pixel distribution consistent with white �� � � noise + uniform leakage current. ���� ���� ��� � �� ��� ��� ��� � ����� 11
ββ coincidences 57 days of data in 1 CCD: 64 keV 1.2 MeV 210 Pb 210 Bi 210 Po 210 Pb < 37 kg -1 d -1 τ 1/2 = 5 d (95% C.L.) 0.22 MeV 1.7 MeV +110 32 Si = 80 kg -1 d -1 32 Si 32 P 32 S -65 (95% C.L.) τ 1/2 = 14 d 32 Si - 32 P candidate JINST 10 P08014 E 1 = 114.5 keV Cluster #79 Δ t = 35 days (x o , y o ) Decay point E 2 = 328.0 keV 12
DAMIC100 • Seven CCDs (~40 g) running at SNOLAB since Jan 2017 . • Already have ~6 kg-day of data with 5-15 dru total background rate. Analysis ongoing. DAMIC-1K 6k x 6k pixels, 1 mm thick ≈ 20 g / CCD ≈ 50 CCDs / 1 Kg • A 1 kg detector built with existing technology. DAMIC100 • 4k x 4k Sub-e - resolution, 2 e - threshold. • Background improvement to 0.1 dru: -Improved design for background suppression. Silicon wafer -Strict handling and packaging procedures. -Baking of wafers during/after fabrication to remove 3 H. 13
SENSEI LDRD at Fermilab (PI Tiffenberg): Skipper CCDs (LBNL design) successfully tested with sub e - noise. X-ray spectroscopy demonstrated. arXiv:1706.00028 Non destructive “skipper” readout : Perform N uncorrelated measurements of the same pixel. Noise decreases by ~1/ √ N . Technology will allow 2 e - (few eV) threshold. Reference Δ V Signal Measure Δ V N times. 14
DAMIC Program DM-nucleus SI coherent scattering DM-e Scattering via Ultra-light Hidden Photon 35 − 10 2 - WIMP-nucleon cross-section / cm - 36 − 10 - − 37 10 - - 38 − CRESST(2015) 10 52 kg-d - 100 g y, 5 dru, 2e - threshold ) 6 1 0 σ n [cm 2 ] 2 ( 39 ] − C 10 I M - A d D - g k 6 . 0 ) 7 DAMIC-1K - 1 kg y (2020) 1 0 2 - ( 0 0 1 [ C − 40 I M d 10 A - D g k 3 1 - CDMSLite(2015) 41 − - 10 70 kg-d - 42 − 10 - CDMSII-Si JHEP05(2016)046 (2013) DAMIC1K(2020) - − 43 10 1 kg-y LUX(2015) 0.1 dru, 2 e - thres. - 44 − 10 1 10 [ ] m [GeV] χ Also best limits for absorption of hidden photon dark matter. 15
DAMIC Program Direct search: DM-e Scattering via heavy Hidden Photon - m A 0 > 2 M χ Ionization χ χ produced by - g D dark matter - A ’ - electron / e ✏ nucleus - scattering. e − e − ] p p - Accelerators: JHEP05(2016)046 [ - - - DAMIC-1K - 1 kg y (2020) = Look for electron’s missing - momentum ( LDMX ) or χ [ ] interacting directly ( BDX ). 16
Conclusion • CCDs are low-radioactivity, low-noise particle detectors whose response to ionizing radiation has been thoroughly characterized . • DAMIC has placed competitive dark matter search results (WIMPs + hidden photons) with early R&D data. • Established discrimination techniques to measure and suppress backgrounds (esp. dominant 32 Si). • Ongoing R&D efforts for a DAMIC-1K : 50 skipper CCDs for a 1 kg detector with 2 e - threshold to search for low-mass dark matter by DM-nucleon and DM-electron scattering. 17
Thank you! 18
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