Energy Calibration and Performance of HPGe Detectors in the LEGEND-200 Experiment
Pith reviewed 2026-05-22 01:50 UTC · model grok-4.3
The pith
Optimized energy reconstruction for LEGEND-200 HPGe detectors reaches 2.47 keV resolution at 2039 keV with weekly peak stability below 0.05 keV.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that the energy calibration procedures, based on weekly 228Th source calibration runs for peak-shape modeling together with systematic corrections for residual non-linearities and energy bias, yield an optimized energy reconstruction with a combined average resolution of (2.47 ± 0.08) keV at Qββ = 2039 keV. Weekly variations of calibration peak positions remain below 0.05 keV for energies up to 2614.5 keV, indicating high stability of the energy scale over time and across detectors.
What carries the argument
The digital signal processing pipeline with peak-shape modeling from weekly 228Th calibrations and applied systematic corrections for non-linearities.
If this is right
- The energy scale maintains stability with variations below 0.05 keV up to 2614.5 keV across the full detector array.
- Systematic corrections remove residual non-linearities and energy bias in the region of interest around 2039 keV.
- This level of resolution and stability supports reliable identification of events at the neutrinoless double beta decay Q-value.
- The procedures enable the first unblinding of data with quantified energy uncertainties.
Where Pith is reading between the lines
- The same weekly calibration approach could be monitored over longer campaigns to check for slow drifts not captured in short-term data.
- The reported resolution and stability metrics provide a benchmark that other low-background germanium arrays could adopt for rare-event searches.
- If the corrections remain effective, the experiment gains margin to tighten background rejection cuts without losing signal efficiency.
Load-bearing premise
The peak-shape modeling from weekly 228Th calibrations and the applied systematic corrections fully capture and remove residual non-linearities and energy biases in the region of interest for all detectors without unaccounted time-dependent or detector-specific effects.
What would settle it
Detection of a calibration peak position shift larger than 0.05 keV or an average resolution exceeding 2.55 keV at 2039 keV in any weekly 228Th run would falsify the reported performance.
read the original abstract
This paper describes the energy scale procedures and germanium detectors performance in the LEGEND-200 experiment, a critical component for the first unblinding in the search for neutrinoless double beta decay. We detail the digital signal processing pipeline, the methodologies for peak-shape modeling and energy calibration procedures utilizing weekly $^{228}$Th source calibration runs. The optimized energy reconstruction achieves a combined average resolution of $(2.47 \pm 0.08)$~keV at $Q_{\beta\beta} = 2039$~keV. The weekly variation of calibration peak positions are below 0.05~keV for energies up to 2614.5~keV, showing a high stability of the energy scale over time and across detectors. Furthermore, systematic corrections effectively address residual non-linearities and energy bias in the region of interest.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript describes the energy calibration and performance of HPGe detectors in the LEGEND-200 experiment. It details the digital signal processing pipeline, peak-shape modeling from weekly 228Th source calibrations, and energy calibration procedures. The optimized reconstruction achieves a combined average resolution of (2.47 ± 0.08) keV at Qββ = 2039 keV, with calibration peak positions varying by less than 0.05 keV up to 2614.5 keV and systematic corrections applied to address residual non-linearities and energy biases in the region of interest.
Significance. If the reported resolution, stability, and corrections hold under scrutiny, this work is significant for the LEGEND-200 0νββ search. Precise energy scale and resolution at Qββ are load-bearing for background discrimination and signal extraction in the first unblinding; the stability metric and correction procedures directly inform the energy-scale uncertainty budget.
major comments (1)
- Abstract: The assertion that 'systematic corrections effectively address residual non-linearities and energy bias in the region of interest' is load-bearing for the central performance claim yet lacks quantitative validation such as residual distributions, cross-checks on independent physics lines, or blinded data. The <0.05 keV stability is reported only on calibration peaks; without explicit tests for detector-specific or time-dependent residuals at 2039 keV, a small unaccounted bias remains possible.
minor comments (2)
- Clarify how the combined average resolution is computed across detectors (e.g., weighted mean, number of detectors included) and whether the quoted uncertainty incorporates all systematic contributions.
- Provide explicit definitions or references for the peak-shape model parameters used in the weekly 228Th fits to improve reproducibility.
Simulated Author's Rebuttal
We thank the referee for their careful review of our manuscript on the energy calibration and performance of HPGe detectors in LEGEND-200. We appreciate the recognition of the work's significance for the 0νββ search and address the major comment below with a point-by-point response.
read point-by-point responses
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Referee: Abstract: The assertion that 'systematic corrections effectively address residual non-linearities and energy bias in the region of interest' is load-bearing for the central performance claim yet lacks quantitative validation such as residual distributions, cross-checks on independent physics lines, or blinded data. The <0.05 keV stability is reported only on calibration peaks; without explicit tests for detector-specific or time-dependent residuals at 2039 keV, a small unaccounted bias remains possible.
Authors: We agree that additional quantitative validation would strengthen the presentation of the systematic corrections. The manuscript describes the digital signal processing, peak-shape modeling from 228Th calibrations, and the application of energy-dependent corrections for non-linearities. The reported stability (<0.05 keV) is derived from weekly calibration peaks up to 2614.5 keV, which bracket the region of interest. To address the comment, we will revise the text and figures to include explicit residual distributions after corrections and cross-checks against independent gamma lines in the physics data. We note that the corrections are applied uniformly across detectors and time periods, with the average resolution of (2.47 ± 0.08) keV at 2039 keV already incorporating these adjustments. However, explicit tests on blinded data are not possible at this stage, as the procedures are being finalized in preparation for the first unblinding. revision: partial
- Provision of validation results using blinded data, which is not available prior to the first unblinding of the 0νββ search.
Circularity Check
No circularity: experimental calibration report with independent data-driven performance metrics
full rationale
The paper describes standard energy calibration procedures for HPGe detectors using weekly 228Th source runs, peak-shape modeling, and systematic corrections to report measured resolution and stability. No derivation chain exists that reduces a claimed result to its own fitted inputs by construction; the quoted resolution (2.47 ± 0.08 keV at 2039 keV) and peak-position stability (<0.05 keV) are direct empirical outcomes from calibration data, not predictions forced by self-definition or self-citation. The central claims rest on observable detector performance rather than any load-bearing ansatz, uniqueness theorem, or renaming of prior results. This is a self-contained experimental methods paper with no evident circular steps.
Axiom & Free-Parameter Ledger
free parameters (1)
- energy scale parameters
axioms (1)
- domain assumption Weekly 228Th source runs provide representative sampling of detector response in the region of interest.
discussion (0)
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