Measurement of low energy ionization signals from Compton scattering in a CCD dark matter detector

Abstract

An important source of background in direct searches for low-mass dark matter particles are the energy deposits by small-angle scattering of environmental $\gamma$ rays. We report detailed measurements of low-energy spectra from Compton scattering of $\gamma$ rays in the bulk silicon of a charge-coupled device (CCD). Electron recoils produced by $\gamma$ rays from ${}^{57}$Co and ${}^{241}$Am radioactive sources are measured between 60 eV and 4 keV. The observed spectra agree qualitatively with theoretical predictions, and characteristic spectral features associated with the atomic structure of the silicon target are accurately measured for the first time. A theoretically-motivated parametrization of the data that describes the Compton spectrum at low energies for any incident $\gamma$-ray flux is derived. The result is directly applicable to background estimations for low-mass dark matter direct-detection experiments based on silicon detectors, in particular for the DAMIC experiment down to its current energy threshold.

arXiv comment8 pages, 9 figures

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• Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection
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• Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs
• Relativistic Impulse Approximation in Compton Scattering
• Relativistic Impulse Approximation in the Atomic Ionization Process induced by Millicharged Particles
• Search for inelastic WIMP-iodine scattering with COSINE-100
• Compton Scattering Energy Spectrum for Si and Ge Systems
• Measurement of the Compton scattering in germanium with a p-type point-contact germanium detector for dark matter detection
• Characterization of the background spectrum in DAMIC at SNOLAB
• Revisiting the Dark Matter Interpretation of Excess Rates in Semiconductors