CENPA Center for Experimental Nuclear Physics and Astrophysics ! 1 - - PowerPoint PPT Presentation
Dark matter search results from DAMIC at SNOLAB Alvaro E. Chavarria University of Washington CENPA Center for Experimental Nuclear Physics and Astrophysics ! 1 Outline Charge-coupled devices to search for dark matter. Response of
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Center for Experimental Nuclear Physics and Astrophysics
University of Washington
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Device is “exposed,” collecting charge until user commands readout
±
Ionizing particle Free charge carriers Fully depleted substrate
15 µm 675 µm
z x x z y σxy σxy ~ z
Silicon band-gap: 1.2 eV Mean energy for 1 e-h pair: 3.8 eV Standard fabrication in semiconductor industry and easy cryogenics (~100 K)
5 10 15 20 25 30 Energy measured by pixel [keV] 30 25 20 15 10 5 50 pixels 4180 4190 4200 4210 4220 1280 1290 1300 1310 1320 1330 Muon
α
Electron Low-energy candidates
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26 − 13 − 13 26 1 10
2
10
3
10
Energy / eV
! = 5.9 eV = 1.6 e- Pixel charge distribution particle identification and background characterization Very low noise and dark current lowest dark current ever measured in a silicon detector: 5x10-22 A/cm2 (at 140 K)
15x15 µm2 pixels
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/ pixels
xy
σ 0.2 0.4 0.6 0.8 1 1.2 1.4 Energy / keV 5 5.2 5.4 5.6 5.8 6 6.2 6.4 6.6 6.8 7 20 40 60 80 100 120 140 160 180 200
from front and back
α
Mn K
Front Back
]
ee
Ionization signal [keV
1 −
10 1 10 )
ee
k(E) / k(5.9 keV 0.96 0.98 1 1.02 1.04 1.06 1.08
X-rays Optical photons
x [pix] 1380 1400 1420 1440 1460 y [pix] 1580 1585 1590 1595 1600 1605 1610 1615 Ionization [keVee] >6 2 4
z reconstruction with X rays and cosmic rays CCD linearity down to 40 eVee with
]
nr
[keV
r
E
1 10
]
ee
[keV
e
E
1 −
10 1 10
Dougherty (1992) Gerbier et al. (1990) Zecher et al. (1990) Be (2016)
9Sb-
124Antonella (2016) Lindhard, k=0.15
/ ndf
2
0.74 (0.06)
f 0.01
(0.3)
f 0.02
f(3.2) 0.02
y offset 1.0
]
ee
[keV
e
E
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 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
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Single-recoil spectrum very similar to signal from 3 GeV WIMP. End-point = 3.2 keVr Calibration down to 60 eVee
keV neutrons from 9Be(γ,n) reaction.
spectra, ionization efficiency was measured to be lower than predicted by Lindhard model.
energies.
/ pixels
xy
σ 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.005 0.01 0.015 0.02 0.025
Simulation SbAl + FullBe
Monte Carlo reproduces σxy distribution at low energies
Number of events per bin Data <0.15 keVee Simulation
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Energy [keV] 5 6 7 8
1x10 1x1
5510 5515 5520 5525 5530 5535 5540 5545 1640 1660 1680 1700 1720 1740
Pixels can be readout in “groups” and the total charge estimated in a single measurement. Less pixels but same noise per pixel! 3x3 1x1
55Fe from back:
Data shows clear improvement in energy resolution Loss of x, y and z information α-β coincidence
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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
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(1 CCD sandwiched in ancient lead).
(each image acquisition is followed by a “blank” exposure).
characterization in 1x1 format.
search in 1x100 format.
and detector studies (e.g., 125 K
preparation for DAMIC-M.
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Pixel distribution of 200 g-d of data in 100 ks exposures Bulk leakage current at the level
CCD 1 CCD 2 CCD 3 CCD 4 CCD 5 CCD 6 CCD 7
leakage current.
leakage-only hypothesis + signal from DM-e interactions. (Before 4 e- mm-2 d-1 at 105 K)
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arXiv:1907.12628
Best exclusion limit for the absorption of hidden photons with masses 1-10 eV/c2 Best exclusion limits for the scattering of dark matter particles with masses <5 MeV/c2
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ΔLL = ℒn - ℒs
Gauss signal + flat noise flat noise
window across the image.
Example of one event E = 0.14 keV, σ = 0.5 ΔLL = -130
For every event we have its statistical significance ΔLL above noise, its amplitude (E, energy) and its spread (σx proportional to z)
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using a simple Poisson model.
clusters.
selection efficiency.
10% efficiency at 50 eVee analysis threshold
dLL dLL
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0.2 0.4 0.6 0.8 1 1.2 1.4 ]
ee
Energy [keV 0.2 0.4 0.6 0.8 1 1.2 [pixels]
x
σ
Comparison of Back Exponential and WIMP Signal
=0.5 keV α Back Surface Exponential,
WIMP Signal, M=2 GeV c
0.2 0.4 0.6 0.8 1 1.2 1.4 ]
ee
Energy [keV 0.2 0.4 0.6 0.8 1 1.2 [pixels]
x
σ 0.5 1 1.5 2 2.5 3 3.5 4
Background model
Monte Carlo. Two-D (E, σx) fit to data above 6 keVee with constraints from known radioactive contaminants. D. Baxter’s presentation from yesterday!
the active region, e.g., implanted 210Pb or 3H migration. Reconstructed depth allows to distinguish from WIMP signal.
Back Front ~5 d.r.u. Bulk
22Na
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signal to search for dark matter.
systematic uncertainties.
Results soon!
model and full analysis to generate expected sensitivity.
WIMPs with masses 1–2 GeV/c2.
fraction of CDMS II-Si.
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technology for dark matter direct detection.
for an experiment with potential for discovery.
under analysis. Expect results soon.
later today.
DAMIC Collaboration
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