CCD Dark Current Might Have Traces of Dark Matter

In the past, pixel dark current has been used for various purposes: identifying traps and defects (dark current spectroscopy), generating random numbers, measuring temperature, forensic picture analysis, random telegraph noise analysis, etc. One could think that nothing else can be in it. However, there appears to be one more thing. A recent Fermi Lab paper examines CCD dark current for the traces of Dark Matter.

Arxiv.org paper "SENSEI: First Direct-Detection Constraints on sub-GeV Dark Matter from a Surface Run" by Michael Crisler, Rouven Essig, Juan Estrada, Guillermo Fernandez, Javier Tiffenberg, Miguel Sofo Haro, Tomer Volansky, and Tien-Tien Yu:

"The Sub-Electron-Noise Skipper CCD Experimental Instrument (SENSEI) uses the recently developed Skipper-CCD technology to search for electron recoils from the interaction of sub-GeV dark matter particles with electrons in silicon. We report first results from a prototype SENSEI detector, which collected 0.019 gram-days of commissioning data above ground at Fermi National Accelerator Laboratory. These commissioning data are sufficient to set new direct-detection constraints for dark matter particles with masses between ~500 keV and 4 MeV."

Yonit Hochberg (Hebrew University of Jerusalem) review "Direct Detection of Dark Matter" explains the detection principle (DM means Dark Matter in the slides):

The Skipper CCD used in this experiment has been presented in 2017 Arxiv.org paper "Single-electron and single-photon sensitivity with a silicon Skipper CCD" by Javier Tiffenberg, Miguel Sofo-Haro, Alex Drlica-Wagner, Rouven Essig, Yann Guardincerri, Steve Holland, Tomer Volansky, and Tien-Tien Yu. The group was able to achieve an impressive performance, such as pixel dark current of 1 electron in 3 years:

"We have developed a non-destructive readout system that uses a floating-gate amplifier on a thick, fully depleted charge coupled device (CCD) to achieve ultra-low readout noise of 0.068 e- rms/pix. This is the first time that discrete sub-electron readout noise has been achieved reproducibly over millions of pixels on a stable, large-area detector. This allows the precise counting of the number of electrons in each pixel, ranging from pixels with 0 electrons to more than 1500 electrons. The resulting CCD detector is thus an ultra-sensitive calorimeter. It is also capable of counting single photons in the optical and near-infrared regime. Implementing this innovative non-destructive readout system has a negligible impact on CCD design and fabrication, and there are nearly immediate scientific applications. As a particle detector, this CCD will have unprecedented sensitivity to low-mass dark matter particles and coherent neutrino-nucleus scattering, while astronomical applications include future direct imaging and spectroscopy of exoplanets."