Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

Abstract

Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of $\mathcal{O}(1\mathrm{eV})$. In this regime, ionization signals from small-angle Compton scatters of environmental $\gamma$-rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23eV. A skipper charge-coupled device (CCD) with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a ${}^{241}$Am $\gamma$-ray source over several months. Features associated with the silicon K, L${}_1$, and L${}_{2,3}$-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5keV. The data are in better agreement with $ab$ $initio$ calculations originally developed for X-ray absorption spectroscopy.

12 pages, 10 figures

References in corpus (5)

• Search for Low-Mass WIMPs with SuperCDMS
• Single-electron and single-photon sensitivity with a silicon Skipper CCD
• Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB
• Ionization Yield in Silicon for eV-Scale Electron-Recoil Processes
• Measurement of low energy ionization signals from Compton scattering in a CCD dark matter detector

Cited by in corpus (12)

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• SENSEI: First Direct-Detection Results on sub-GeV Dark Matter from SENSEI at SNOLAB
• Search for Daily Modulation of MeV Dark Matter Signals with DAMIC-M
• Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs
• Low-Energy Backgrounds in Solid-State Phonon and Charge Detectors
• The DAMIC-M Low Background Chamber
• Low-Energy Calibration of SuperCDMS HVeV Cryogenic Silicon Calorimeters Using Compton Steps
• Shake-up and shake-off effects in neutrinoless double-beta decay
• Multi-Amplifier Sensing Charge-coupled Devices for Next Generation Spectroscopy
• Measurement of the Compton scattering in germanium with a p-type point-contact germanium detector for dark matter detection
• Nuclear Recoil Identification in a Scientific Charge-Coupled Device
• Light-tight skipper-CCDs for X-ray detection in space