University of Maryland March, 23 rd 2017 DAMIC and a kg-size CCD experiment Paolo Privitera for the DAMIC Collaboration (Photo image: particle tracks in a DAMIC CCD )
CCD principle Metal-Oxide-Semiconductor capacitor +V Moving charge from pixel to pixel Metal gate Si oxide (insulator) 1 1 1 1 1 n-type Si (buried channel) 2 2 2 2 2 - p-type Si 3 3 3 3 3 + electron-hole pairs generated by a photon or ionizing particle “vertical clocks” readout time Charge motion Output amplifier Charge motion Correlated Double Sampling “horizontal clocks” (faster)
6 cm Copper frame CCD Clocks, Bias, Wire bonds 2k x 4k and Signal cable 1) Sizable mass (high resistivity, thick CCDs designed by LBNL) A DAMIC CCD has an active area of 6 cm x 6 cm, 16 Mpixel (each 15 µm x 15 µm) and a record thickness of 675 µm for a total of 5.9 g mass DAMIC100 currently taking data at the SNOLAB underground laboratory 3
2) Unprecedented low energy threshold • Negligible noise contribution from dark current fluctuations (dark current < 0.001 e/pixel/day with CCD cooled at 120 K). Readout noise dominant contribution. exposure blank (taken after exposure) • A readout noise of ≈ 2 e- is achieved by slow CCD readout ( ≈ 10 min / 16 Mpix image). 3.6 eV to produce 1 e-hole pair 5 10 Image Blank Gaussian fit 4 10 mean = -0.003 � 0.001 Entries per bin = 1.827 0.001 � � 3 10 • Very long exposures (8 hours!) to 2 10 minimize the n. of noise pixels above SNOLAB data the energy threshold 10 1 � 10 0 10 20 30 40 - Pixel Value [e ] 4
4) Unique spatial resolution: 3D position reconstruction and particle ID a muon piercing a DAMIC CCD single muon track σ xy ≈ Z : fiducial volume definition and surface event rejection = 750 µm • “ Worms”: straggling electrons • Straight tracks: minimum ionizing particles • MeV charge blobs: alphas • Diffusion-limited clusters: low-energy X-rays, nuclear recoils • CCD spatial resolution provides a unique handle to the understanding of the background 5
DAMIC @ SNOLAB 16 Mpix CCD 5.8 g Poly- 6 cm VIB ethylene Lead Kapton Copper Lead block Kapton signal cable module signal cable Cu box with CCDs Cu vacuum vessel 6
DAMIC results Measurement of radioactive contamination in the high-resistivity silicon CCDs of the DAMIC experiment JINST 10 (2015) P08014 Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB Phys. Rev. D 94, 082006 (2016) First direct detection constraints on eV-scale hidden-photon dark matter with DAMIC at SNOLAB arXiv:1611.03066 accepted by Phys. Rev. Lett. Measurement of the ionization produced by sub-keV silicon nuclear recoils in a CCD dark matter detector Phys. Rev. D 94, 082007 (2016) Antonella: A nuclear-recoil ionization-efficiency measurement in silicon at low energies arXiv:1702.00873 7
Radiogenic backgrounds E = 6.8 MeV E = 8.8 MeV E = 5.4 MeV RUNID= 491, EXTID= 6, cluster_id= 1388 RUNID= 345, EXTID= 6, cluster_id= 1801 RUNID= 490, EXTID= 6, cluster_id= 1345 506 5000 504 5000 5000 504 4500 504 4500 502 4500 502 4000 4000 502 4000 500 3500 3500 500 3500 500 498 3000 3000 498 3000 498 496 2500 2500 2500 496 496 494 2000 2000 2000 494 494 1500 1500 492 1500 492 492 1000 1000 1000 490 490 490 500 500 500 488 488 0 488 0 0 6048605060526054605660586060606260646066 6050 6052 6054 6056 6058 6060 6062 6064 6066 60506052 60546056 605860606062 60646066 Δt = 17.8 d 2 Δt = 5.5 h 3 1 three α at the same loca<on! Powerful method to measure U/Th bkg Example α + β in the bulk – ppt limits of 2015 JINST 10 P08014 2 Bragg peak 1 3 Not seen 8
Nuclear recoil calibration 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 ] 1000 -1 Data - full BeO ) ee Number of nuclear recoils [(10 eV Best-fit with Monte Carlo spectrum 800 Single-recoil spectrum 2 � / ndf 142 / 154 600 very similar to signal Prob 0.74 -1 f (0.06) 0.63 � 0.01 from 3 GeV WIMP. -1 f (0.3) 1.94 0.02 � PRD94 082007 400 f(3.2) End-point = 3.2 keV r 0.61 � 0.02 y offset 1.4 1.0 � Calibration down 200 to 60 eV ee . 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 E [keV ] e ee 9
WIMPs search 2 All data 1 × 1 1 × 100 Surface (sim) 1.8 Measure E and σ xy for candidates 1.6 every cluster event. 1.4 1.2 σ xy [pix] 1 0.8 σ xy ≈ proportional to depth of 0.6 0.4 interaction in the bulk silicon 0.2 0 0 1 2 3 4 5 6 7 8 9 10 0 4 8 12 16 E [keV ee ] Entries limited exposure taken during R&D phase (bkg. ≈ 30 dru) demonstration of DAMIC sensitivity to low-mass Dark Matter NOTE: current bkg. ≈ 5 dru 10
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 - arXiv:1611.03066 - - Ionization - dark accepted by PRL �� � �� matter. �� � �� Hidden Photon �� � �� � �� � ������� ������� � ����� ����� �� � �� ����� ���� �� � ���� ��� � � ����� ���� ������� ���� � ��� � � � � � � � ������ �� ������ ������� ���� �� � �� �� � ��� � � ����� ������� ������� � ��� � � � � � � � ����� ����� ���� ���������� �� � �� �� � �� � �� � � � ���� � � � �� � Pixel distribution consistent with white �� � � noise + uniform leakage current. ���� ���� ��� � �� ��� ��� ��� � ����� 11
DAMIC now • Already achieved radioactive background ( 5 dru ) and low-noise ( <2 e- ) performance for a larger detector. • Stack of 16 Mpix CCDs: DAMIC100 in current SNOLAB vacuum vessel and shielding. • Installation took place in January, results with ≈ 10 kg day of data expected in 2017. • Ongoing R&D for thicker, larger-area CCDs for a lower-noise, lower-background kg-size detector. DAMIC-1K • A kg-size experiment with 0.1 dru background and ≤ 2e- threshold • To lead the exploration of WIMPs and dark sector candidates in the low-mass DM parameter space 12
DAMIC-1K and WIMPs WIMP-nucleon σ [cm 2 ] DAMIC-1K N th = 2 e - SuperCDMS-HV Si forecast (arXiv:1610.00006v1) N th = 0.2 e - DAMIC-1K (taking same assumptions of SuperCDMS) WIMP mass [GeV c -2 ] 13 DAMIC-1K not limited by 32 Si bkg.
DAMIC-1K and dark sector 14
DAMIC-1K and dark sector All Experiments ( Kinetic Mixing + Elastically Coupled DM ) LHC 10 - 4 10 - 5 LEP 10 - 6 DarkLight BaBar E787 / 949 @ BNL @ JLab 10 - 7 y = � 2 � D ( m � / m A' ) 4 PADME @ LNF MiniBooNE 10 - 8 @ FNAL VEPP - 3 10 - 9 @ BINP MMAPS @ Cornell 10 - 10 BDX @ JLab Belle II E137 10 - 11 NA64 DAMIC-1K Scalar Relic Target @ CERN 10 - 12 LSND Complementary 10 - 13 Fermion Relic Target to accelerator LDMX @ SLAC searches! 10 - 14 (NOTE: accelerator and direct 10 - 15 detection limits comparable only for certain models) 10 - 16 10 2 10 3 1 10 m � ( MeV ) 15
DAMIC-1K technical challenges • A kg-size DAMIC can be built with the existing technology Silicon wafer 6k x 6k pixels, 1 mm thick DALSA has ≈ 20 g / CCD confirmed the DAMIC100 4k x 4k feasibility fabrication ≈ 50 CCDs / 1 Kg of these larger and thicker CCDs • Background from a few dru to a fraction of dru. external bkg.: improved design, materials (e.g. electroformed copper), strict procedures (silicon storage underground, radon, surface contamination) internal bkg.: cosmogenic 32 Si and tritium
DAMIC-1K background • Cosmogenic 32 Si rate will be accurately measured by the current detector at SNOLAB ≈ 1 dru (dominant bkg. in SuperCDMS); rejected in DAMIC-1K by spatial correlations • Tritium expected to be the spectrum measured dominant bkg. for DAMIC-1K. in the lab A measurement of its rate may be within reach of the current DAMIC detector at SNOLAB (so far only estimates are used for forecasts) 17
DAMIC-1K sub-e - noise • Skipper readout Already achieved on a small size CCD (LBNL design; LDRD at Fermilab) See J. Tiffenberg SENSEI talk • Digital filtered CDS does not require a new CCD design, could already significantly improve sensitivity of DAMIC100 18
The DAMIC-1K experiment • DAMIC Collaboration CAB, Fermilab, LPNHE, SNOLAB, U Chicago, U Michigan, UNA, UNAM, UFRJ, U Zürich Several new groups interested in joining DAMIC-1K (PNNL, Denmark, France, Germany, Spain) • Timing 2017-2018 R&D for sub-e - noise/background measurements; DAMIC100 results; finalize detector design 2018-2019 components validation (test at SNOLAB) 2019-2020 Construction • Budget ≤ 3 M$ (construction) 19
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