measurement of single-scatter compton electrons … of...measurement of single-scatter compton...
TRANSCRIPT
Measurement of Single-Scatter Compton Electrons and Dark Current in DAMIC CCDs
Karthik Ramanathan University of Chicago Kavli Institute for Cosmological Physics SNOLAB Users Meeting 2016
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DAMIC in brief } DAMIC – Dark Matter In CCDs } Exploit properties of CCDs to detect & analyze particles } WIMP – Weakly Interacting Massive Particle
} Nuclear Recoil
} DAMIC-100 detector currently being deployed at SNOLAB
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CAB, Fermilab, LPNHE, SNOLAB, U Chicago, U Michigan, UNA, UNAM, UFRJ, U Zürich
Detector & CCD
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Low Noise
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Ø Pixel read noise σ ≈ 2e-
Ø Single pixel energy threshold < 100 eV
Latest Exclusion Plot
5 Aguilar-Arevalo et al. 2016, arXiv:1607.07410
Testbed (UChicago)
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cv
cv
cv
cv
Motivation & Approach
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} Characterize response of detector at low energy to dominant background – radiogenic γ-‐rays and demonstrate O(10ev) threshold
} Expose to γ-‐ray source } Compton features
Data: NIST PhysRefData XCOM
Cobalt 57 122 KeV γ 6x Cross Section
CO-57 Selection
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Measured Spectrum in DAMIC (UC)
122 keV & 136 keV peaks
1st edge: 39.5 keV
2nd edge: 47.5 keV
Fluorescence peaks
Expected Spectrum
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} Visible Step features
} Silicon Binding Energies
MCNP Simulation Model
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Data & Binning
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charge of several pixels can be added together before moving it to the readout node
some loss of spatial resolution but improved signal to noise (same readout noise but more charge in a binned pixel)
Results
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60 eVee
e- backscatter?
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Excess events
e- backscatter?
Takeaway
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} These measurements demonstrate DAMIC's resolution down to ~60 eV and characterize the spectrum of the major background for the DAMIC WIMP search, low-energy signals from electrons Compton scattered by radiogenic γ-rays.
Dark Current Data
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} Dark Current: } Thermally generated electrons will contribute to overall signal
measured
} Accurate measurements of DC can not only aid calibration but can also help constrain more exotic DM models: } Hidden Photons, Axions, ALPs
Measuring DC
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Results
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Image Overscan
R ~ 1.4E-2 [e- /px/day]
• December 2015 • 9 images • 17 hr exposure/image
Applications
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• DC provides a floor for CCD interactions à Assume all DC were these exotic particles à Constraint on mixing parameter
Preliminary Results
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Questions?
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