Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs

Abstract

We present results from a 3.25 kg-day target exposure of two silicon charge-coupled devices (CCDs), each with 24 megapixels and skipper readout, deployed in the DAMIC setup at SNOLAB. With a reduction in pixel readout noise of a factor of 10 relative to the previous detector, we investigate the excess population of low-energy events in the CCD bulk previously observed above expected backgrounds. We address the dominant systematic uncertainty of the previous analysis through a depth fiducialization designed to reject surface backgrounds on the CCDs. The measured bulk ionization spectrum confirms the presence of an excess population of low-energy events in the CCD target with characteristic rate of $\sim 7$ events per kg-day and electron-equivalent energies of $\sim 80$eV, whose origin remains unknown.

8 pages, 4 figures

References in corpus (12)

• SENSEI: Direct-Detection Results on sub-GeV Dark Matter from a New Skipper-CCD
• Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB
• First Constraints from DAMIC-M on Sub-GeV Dark-Matter Particles Interacting with Electrons
• Results on Low-Mass Weakly Interacting Massive Particles from an 11 kg-day Target Exposure of DAMIC at SNOLAB
• EXCESS workshop: Descriptions of rising low-energy spectra
• Absolute measurement of the Fano factor using a Skipper-CCD
• SENSEI: Characterization of Single-Electron Events Using a Skipper-CCD
• Cosmogenic activation of materials
• Measurement of low energy ionization signals from Compton scattering in a CCD dark matter detector
• Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection
• Latest observations on the low energy excess in CRESST-III
• Ionization efficiency for nuclear recoils in silicon from $\sim 50$ eV to $3$ MeV

Cited by in corpus (7)

• Probing Benchmark Models of Hidden-Sector Dark Matter with DAMIC-M
• Low-Energy Backgrounds in Solid-State Phonon and Charge Detectors
• The DAMIC-M Low Background Chamber
• Particle background characterization and prediction for the NUCLEUS reactor CE$\nu$NS experiment
• Removal of spallation-induced tritium from silicon through diffusion
• Molecular Dynamics Simulations on Nuclear Recoils in Silicon Crystals towards Single Electron-Hole Pair Ionization Yields
• Modeling the Differential Rate for Signal Interactions in Coincidence with Noise Fluctuations or Large Rate Backgrounds