DAMIC and a kg-size CCD experiment Paolo Privitera for the DAMIC - - PowerPoint PPT Presentation

Paolo Privitera for the DAMIC Collaboration

DAMIC and a kg-size CCD experiment

(Photo image: particle tracks in a DAMIC CCD )

University of Maryland March, 23rd 2017

CCD principle

p-type Si n-type Si (buried channel) Si oxide (insulator) Metal gate Metal-Oxide-Semiconductor capacitor

+V

• +

electron-hole pairs generated by a photon or ionizing particle

Charge motion Charge motion

Output amplifier

“vertical clocks” “horizontal clocks” (faster)

Moving charge from pixel to pixel

readout time

Correlated Double Sampling

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

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CCD Wire bonds Clocks, Bias, and Signal cable Copper frame 6 cm 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 2k x 4k

4 blank (taken after exposure) exposure

• Very long exposures (8 hours!) to

minimize the n. of noise pixels above the energy threshold

2) Unprecedented low energy threshold

3.6 eV to produce 1 e-hole pair

• Negligible noise contribution from dark current fluctuations (dark current < 0.001

e/pixel/day with CCD cooled at 120 K). Readout noise dominant contribution.

• A readout noise of ≈ 2 e- is

achieved by slow CCD readout (≈ 10 min / 16 Mpix image).

• Pixel Value [e ]

10

• 10

20 30 40 Entries per bin 1 10

2

10

3

10

4

10

5

10

0.001

• = 1.827
• 0.001
• mean = -0.003

Image Blank Gaussian fit

SNOLAB data

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4) Unique spatial resolution: 3D position reconstruction and particle ID σxy ≈ Z : fiducial volume definition and surface event rejection

single muon track

• “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

a muon piercing a DAMIC CCD = 750 µm

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16 Mpix CCD Copper module Kapton signal cable Poly- ethylene Lead 6 cm 5.8 g VIB Lead block Cu box with CCDs Kapton signal cable Cu vacuum vessel

DAMIC @ SNOLAB

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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

Radiogenic backgrounds

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6050 6052 6054 6056 6058 6060 6062 6064 6066 488 490 492 494 496 498 500 502 504 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

60506052 60546056 605860606062 60646066 488 490 492 494 496 498 500 502 504 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

RUNID= 490, EXTID= 6, cluster_id= 1345

6048605060526054605660586060606260646066 488 490 492 494 496 498 500 502 504 506 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

RUNID= 491, EXTID= 6, cluster_id= 1388

E = 5.4 MeV E = 6.8 MeV E = 8.8 MeV 1 2 3 1 2 3 Δt = 17.8 d Δt = 5.5 h three α at the same loca<on! α + β

Bragg peak

Powerful method to measure U/Th bkg in the bulk – ppt limits

Not seen

Example

• f

2015 JINST 10 P08014

/ ndf

2

• Prob

0.74 (0.06)

• 1

f 0.01

• 0.63

(0.3)

• 1

f 0.02

• 1.94

f(3.2) 0.02

• 0.61

y offset 1.0

• 1.4

]

ee

[keV

e

E

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

]

• 1

)

ee

Number of nuclear recoils [(10 eV

200 400 600 800 1000

142 / 154 Best-fit with Monte Carlo spectrum Data - full BeO

PRD94 082007

CCD Lead shielding

3He counter

Source Vacuum chamber a) Cross-section of setup BeO base BeO cylinder BeO cap Table Table Activated antimony rod b) 124Sb-9Be source detail 20 cm 2.75 cm

24 keV neutrons from

9Be(γ,n)

reaction

Single-recoil spectrum very similar to signal from 3 GeV WIMP. End-point = 3.2 keVr

Calibration down to 60 eVee.

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Nuclear recoil calibration

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WIMPs search

2 4 6 8 10 1 3 5 7 9 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 E [keVee] σxy [pix]

1×1 1×100 Surface (sim)

4 8 12 16 Entries

All data candidates

Measure E and σxy for every cluster event. σxy ≈ proportional to depth of interaction in the bulk silicon

limited exposure taken during R&D phase (bkg. ≈ 30 dru) demonstration of DAMIC sensitivity to low-mass Dark Matter NOTE: current bkg. ≈ 5 dru

• Absorption
• f hidden-

photon dark matter.

• arXiv:1611.03066

accepted by PRL

~1 week of data with 1 CCD. Leakage current 4 e- mm-2 d-1. Pixel distribution consistent with white noise + uniform leakage current.

Hidden Photon Ionization

• e-
• 675 µm
• Si bulk

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Hidden photon search

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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.

• A kg-size experiment with 0.1 dru background and ≤ 2e- threshold

DAMIC-1K

• To lead the exploration of WIMPs and dark sector candidates in the

low-mass DM parameter space

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DAMIC-1K and WIMPs

WIMP mass [GeV c-2] WIMP-nucleon σ [cm2] DAMIC-1K Nth = 2 e- DAMIC-1K

(taking same assumptions of SuperCDMS)

SuperCDMS-HV Si forecast

(arXiv:1610.00006v1)

Nth = 0.2 e-

DAMIC-1K not limited by 32Si bkg.

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DAMIC-1K and dark sector

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DAMIC-1K and dark sector

Scalar Relic Target Fermion Relic Target

BaBar LHC LEP BDX@JLab E787/949@BNL PADME@LNF LDMX@SLAC VEPP-3 @BINP NA64 @CERN MMAPS @Cornell DarkLight @JLab

Belle II

MiniBooNE @FNAL

LSND E137

1 10 102 103 10-16 10-15 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4

m (MeV) y = 2D (m /mA')4

All Experiments (Kinetic Mixing + Elastically Coupled DM)

DAMIC-1K

Complementary to accelerator searches!

(NOTE: accelerator and direct detection limits comparable only for certain models)

DAMIC-1K technical challenges

• A kg-size DAMIC can be built with the existing technology

Silicon wafer

6k x 6k pixels, 1 mm thick ≈ 20 g / CCD ≈ 50 CCDs / 1 Kg

DAMIC100 4k x 4k

DALSA has confirmed the feasibility fabrication

• f 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 32Si and tritium

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DAMIC-1K background

• Cosmogenic 32Si rate will be accurately measured by the current

detector at SNOLAB

• Tritium expected to be the

dominant bkg. for DAMIC-1K. A measurement of its rate may be within reach of the current DAMIC detector at SNOLAB (so far only estimates are used for forecasts) ≈ 1 dru (dominant bkg. in SuperCDMS); rejected in DAMIC-1K by spatial correlations

spectrum measured in the lab

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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

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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)

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Conclusions

• In the last two years DAMIC has established the CCD technology as

a competitive technique for the search of low-mass Dark Matter particles

• DAMIC-1K, a kg-size CCD detector with low background and sub-

electron noise, will explore a new large parameter space, scrutinizing the WIMPs paradigma, as well as dark sector candidates with sensitivity comparable to accelerator searches (for certain classes of models)

• The DAMIC-1K detector is an incremental step of proven

technologies (larger size CCD, sub-electron noise). It will work as specified.

• There are strong synergies between DAMIC-1K and SuperCDMS Si:

measurement of the quenching factor down to the ionization threshold; 32Si “depleted” silicon: DAMIC spatial coincidence technique unique tool to measure residual background.