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arxiv: 2605.30281 · v1 · pith:V3NCZDSQnew · submitted 2026-05-28 · ⚛️ physics.ins-det · astro-ph.IM· hep-ex

Characterization of Spurious Charge in SENSEI Skipper-CCDs

Yikai Wu , Ansh Desai , Sho Uemura , Ana M. Botti , Brenda A. Cervantes-Vergara , Fernando Chierchie , Alex Drlica-Wagner , Rouven Essig
show 11 more authors
Juan Estrada Erez Etzion Guillermo Fernandez Moroni Miqueas Gamero Stephen E. Holland Ian Lawson Steffon Luoma Nathan A. Saffold Miguel Sofo-Haro Javier Tiffenberg Tomer Volansky
This is my paper

Pith reviewed 2026-06-28 23:47 UTC · model grok-4.3

classification ⚛️ physics.ins-det astro-ph.IMhep-ex
keywords spurious chargeSkipper-CCDsingle-electron eventstri-level clockingserial registercharge transferlow-background detectordark matter search
0
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The pith

Spurious single-electron charge in Skipper-CCDs is dominated by the serial register during readout and drops by a factor of seven with tri-level clocking.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Skipper-CCDs search for sub-GeV dark matter and coherent neutrino scattering but are limited by spurious single-electron events generated during charge transfer. The paper measures these events in the SENSEI detector in a shielded underground site and traces the dominant source to the serial register when horizontal clocks remain at constant low voltage between transfers. The authors introduce tri-level clocking, which raises the held-low voltage to an intermediate level to reduce trap-mediated generation. This change cuts the serial-register rate from (2.9 ± 0.1) × 10^{-5} to (4.0 ± 0.4) × 10^{-6} electrons per pixel per image. A reader cares because the method lowers a key background for rare-event searches using existing hardware.

Core claim

In a well-shielded low-background environment, the dominant contribution to spurious charge originates in the serial register during Skipper readout when horizontal clocks are held at constant voltage between pixel transfers. A tri-level clocking scheme raises the held-low phase to an intermediate voltage and reduces the serial-register single-electron density from (2.9 ± 0.1) × 10^{-5} to (4.0 ± 0.4) × 10^{-6} electrons/pixel/image, a factor of ∼7 improvement.

What carries the argument

Tri-level clocking scheme that raises the held-low phase of the horizontal clocks to an intermediate voltage during readout to suppress trap-mediated charge generation in the serial register.

If this is right

  • The serial-register single-electron density drops to (4.0 ± 0.4) × 10^{-6} electrons/pixel/image under tri-level clocking.
  • This technique supplies a practical route to lower backgrounds in present and future Skipper-CCD dark-matter and neutrino experiments.
  • Dominance of the serial register holds only when other backgrounds are controlled by shielding and low-radioactivity materials.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Tri-level clocking could be ported to other Skipper-CCD or CCD-based rare-event detectors to test whether comparable background reductions appear.
  • Lower single-electron rates would directly tighten limits on sub-GeV dark matter interactions by reducing the irreducible background floor.
  • Combining the clocking change with existing shielding or material improvements might produce larger total background reductions than either method alone.

Load-bearing premise

That in the well-shielded low-background environment at the MINOS cavern, other potential sources of single-electron events are negligible compared to the serial register contribution, allowing clean attribution of the measured rates.

What would settle it

Repeating the rate measurements in the same shielded setup but with a different clocking voltage sequence that keeps the low phase unchanged and observing no reduction in single-electron density would falsify the efficacy of tri-level clocking.

Figures

Figures reproduced from arXiv: 2605.30281 by Alex Drlica-Wagner, Ana M. Botti, Ansh Desai, Brenda A. Cervantes-Vergara, Erez Etzion, Fernando Chierchie, Guillermo Fernandez Moroni, Ian Lawson, Javier Tiffenberg, Juan Estrada, Miguel Sofo-Haro, Miqueas Gamero, Nathan A. Saffold, Rouven Essig, Sho Uemura, Steffon Luoma, Stephen E. Holland, Tomer Volansky, Yikai Wu.

Figure 1
Figure 1. Figure 1: FIG. 1. Microscope image showing one corner of a Skipper [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Schematic diagram of spurious charge generation [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Calibrated images of C-module constructed by taking the median of each pixel value across a series of images to [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Serial register charge density distribution of a C-module in surface setup without pixel-pumping (black) and with [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Serial register spurious charge (SRSC) rate measured [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8. Tri-level clocking sequence during pixel transfer and [PITH_FULL_IMAGE:figures/full_fig_p009_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9. Charge distribution of serial register pixels read [PITH_FULL_IMAGE:figures/full_fig_p010_9.png] view at source ↗
read the original abstract

Skipper Charge-Coupled Devices (Skipper-CCDs) are a leading technology in the search for sub-GeV dark matter and coherent elastic neutrino-nucleus scattering. A key background for rare-event searches with these detectors arises from "spurious charge" -- single-electron events generated when charges are transferred through the active region to the serial register, and across the serial register to the readout stage. We present a characterization of spurious charge in both the active region and the serial register of SENSEI Skipper-CCDs, and show that, in a well-shielded low-background environment, the dominant contribution originates in the serial register during Skipper readout, when horizontal clocks are held at constant voltage between pixel transfers. Motivated by this finding, we develop a "tri-level" clocking scheme in which the held-low phase is raised to an intermediate voltage during readout to suppress trap-mediated charge generation. Using the SENSEI detector near the MINOS cavern, we measure a serial-register single-electron density of $(2.9 \pm 0.1) \times 10^{-5}$ electrons/pixel/image under standard SENSEI readout conditions, reduced to $(4.0 \pm 0.4) \times 10^{-6}$ electrons/pixel/image with tri-level clocking -- a factor of $\sim$7 improvement. This technique offers a promising path to lower backgrounds in current and future Skipper-CCD experiments.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 0 minor

Summary. The paper characterizes spurious charge in SENSEI Skipper-CCDs, reporting that in a well-shielded low-background environment the dominant source is the serial register during readout when horizontal clocks are held at constant voltage. It introduces a tri-level clocking scheme that reduces the measured serial-register single-electron density from (2.9 ± 0.1) × 10^{-5} to (4.0 ± 0.4) × 10^{-6} electrons/pixel/image, a factor of ~7 improvement, while also quantifying the smaller active-region contribution.

Significance. If the attribution holds, the result supplies a practical, experimentally demonstrated technique for background reduction in Skipper-CCD searches for sub-GeV dark matter and CEvNS. The manuscript supplies direct rate measurements carrying explicit statistical uncertainties, with explicit separation of active-region versus serial-register contributions obtained in a controlled shielded environment; these quantitative, model-independent data constitute a clear strength.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive evaluation of the manuscript and for recommending acceptance. No major comments were raised in the report.

Circularity Check

0 steps flagged

No significant circularity; results from direct experimental measurements

full rationale

The paper reports direct rate measurements of spurious charge in Skipper-CCDs, isolating serial-register contributions via shielded-environment data and demonstrating a factor-of-7 reduction under tri-level clocking. All central claims carry explicit statistical uncertainties and rest on observed counts rather than any derivation, fit, prediction, or self-citation chain. No equations or steps reduce by construction to inputs; the attribution of dominance to the serial register follows from comparative measurements, not from any self-definitional or fitted-input logic. This is the expected non-finding for a pure characterization study.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental characterization paper. No mathematical derivations, fitted parameters, or postulated entities are involved in the central claim; results rest on direct rate measurements under different clocking conditions.

pith-pipeline@v0.9.1-grok · 5881 in / 1191 out tokens · 30865 ms · 2026-06-28T23:47:58.933476+00:00 · methodology

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Reference graph

Works this paper leans on

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