Skipper Charge-Coupled Device for Low-Energy-Threshold Particle Experiments above Ground

We present experimental results using a single-electron resolution skipper CCD running above ground level to demonstrate the potential of this technology for its use in reactor neutrino observations and other low-energy particle-interaction experiments. Operating conditions and event-selection criteria are provided to decouple most of the background rate at low energies. The majority of this background comes from interactions in the inactive silicon surrounding the active detector volume that ends up in the readout register of the sensor. Our final results are compared with other low-threshold technologies showing a good control of the background for low ionization energies down to five electron-hole pairs. This demonstrates that the skipper CCD proves to be among the best options to measure low-energy and weakly interacting particles at ground level.

Figure 1

(a) Expected number of neutrino events in silicon as a function of the energy threshold of the sensor; the energy unit is in ionization energy after quenching factor corrections. (b) Significance for detecting CEvNS as a function of the background level.

Figure 2

(a) Setup used for the experiment with a short description of the main components. (b) A picture of the CCD installed on the copper tray. An extra copper plate that covers the top part of the sensor is not presented in the image.

Figure 3

Histogram of pixels with charge up to 100 $e^{-}$ after calibration. Single-electron discrimination is observed. The inset shows the same histogram for the first ten peaks.

Figure 4

Morphology of the events in the output image: (a),(b) are the expected events from true interactions in the sensor generated from simulations; (c),(d) serial-register event contributions measured without dumping the collected charge in the active volume to the serial register; and (e),(f) measured events in the active region of the sensor.

Figure 5

(a) Energy spectrum before and after applying the selection criteria to the data (not weighted by the selection efficiency). The first two bins of the spectrum for all the events exceeds the selected maximum value in the $y$ axes. The inset shows the distribution of the selected events with thinner bins at low energy. The error bar in the inset is chosen to have a symmetric coverage probability of 68.25% around the mean value. (b) Efficiency of the selection cuts. (c) Comparison of our results (Skipper-CCD@surface@FNAL) with other low-energy technologies presented in Ref. [30].

Figure 6

Size distribution of events simulated in the active region of the sensor: (a) in the $y$ axis, (b) in the $x$ axis. The bins are normalized by the total number of simulated events.