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arxiv: 2605.20507 · v1 · pith:LD46JAQSnew · submitted 2026-05-19 · ⚛️ physics.ins-det

Procurement and Purification of Liquid Argon for the LEGEND-200 Experiment

Malgorzata Hara\'nczyk , Patrick Krause , Tomasz Mr\'oz , Laszlo Papp , Krzysztof Pelczar , Stefan Sch\"onert , Mario Schwarz , Christoph Vogl
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Grzegorz Zuzel Marco Balata Nina Burlac
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Pith reviewed 2026-05-21 06:49 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords liquid argon purificationLEGEND-200scintillation lifetimecryostat fillingimpurity removalbackground discriminationneutrino detector
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The pith

A copper catalyst and molecular sieve purifier raises liquid argon triplet lifetime from 0.9 to 1.3 microseconds for LEGEND-200.

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

The paper presents a system for purifying liquid argon to the high standards needed for background discrimination in the LEGEND-200 neutrino experiment. It details how liquid argon of initial 5.5 quality was processed using a purifier with copper catalyst and molecular sieve to remove oxygen and water. This process improved the effective scintillation light triplet lifetime from about 0.9 microseconds to 1.3 microseconds. During the filling of the 91-ton cryostat, the measured lifetime reached 1.16 microseconds, with a small drop attributed to nitrogen from one delivery that was controlled by monitoring equipment.

Core claim

The purification system successfully processed liquid argon starting with an effective triplet lifetime of about 0.9 μs to achieve a final purity corresponding to τ_t = 1.3 μs. After filling the LEGEND-200 cryostat with 91 t of this argon, the effective triplet lifetime measured 1.16 μs, with the reduction due to residual nitrogen from an accidentally spoiled delivery that was limited by the monitoring apparatus.

What carries the argument

The liquid argon purifier based on copper catalyst and molecular sieve for removing oxygen and water impurities, along with the LEGEND Liquid Argon Monitoring Apparatus for detecting nitrogen influx.

Load-bearing premise

The copper catalyst and molecular sieve remove oxygen and water impurities effectively without introducing new contaminants that would degrade the scintillation properties.

What would settle it

Observing an effective triplet lifetime remaining at or below 0.9 μs after passing through the purifier would show that the system did not improve the purity as claimed.

Figures

Figures reproduced from arXiv: 2605.20507 by Christoph Vogl, Grzegorz Zuzel, Krzysztof Pelczar, Laszlo Papp, Malgorzata Hara\'nczyk, Marco Balata, Mario Schwarz, Nina Burlac, Patrick Krause, Stefan Sch\"onert, Tomasz Mr\'oz.

Figure 12
Figure 12. Figure 12: Time resolved evolution of the effective triplet life￾time of LAr scintillation (top) and the primary light yield (center) together with the calculated increase in nitrogen con￾centration (bottom). Overall, the nitrogen content increased by 0.9 ppm over the course of 17 hours. Taken from [8] [PITH_FULL_IMAGE:figures/full_fig_p013_12.png] view at source ↗
read the original abstract

LEGEND-200 requires high-purity liquid argon for effective background discrimination. In this paper, we present the design, construction, and performance of a dedicated liquid argon purification system, along with the procurement and purification of liquid argon for filling the LEGEND-200 cryostat to its total capacity of 91 t. The purifier is based on copper catalyst and molecular sieve to remove oxygen and water. Starting with liquid argon of 5.5 quality, featuring an effective scintillation light triplet lifetime $\tau_t$ of about 0.9 $\mu$s, we achieved a final purity corresponding to $\tau_t$ = 1.3 $\mu$s. After complete filling of the LEGEND-200 cryostat, the measured effective triplet lifetime was 1.16 $\mu$s. The notable reduction is caused by a residual nitrogen impurity introduced by an accidentally spoiled liquid argon delivery. An excessive nitrogen influx was prevented by the LEGEND Liquid Argon Monitoring Apparatus (LLAMA), which served as one of the three independent purity monitors during the filling campaign.

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

1 major / 3 minor

Summary. The manuscript reports on the procurement of 91 tonnes of liquid argon and the operation of a purification system consisting of a copper catalyst and molecular sieve for the LEGEND-200 experiment. It details how starting material with τ_t ≈ 0.9 μs was purified to achieve τ_t = 1.3 μs, with post-filling measurement of 1.16 μs due to nitrogen contamination identified by LLAMA and other monitors.

Significance. This technical achievement is significant for enabling the high-purity requirements of LEGEND-200's liquid argon veto system, which is critical for background suppression in the neutrinoless double beta decay search. The experience with large-scale filling and real-time monitoring offers valuable lessons for similar experiments like those in the neutrino or dark matter communities.

major comments (1)
  1. The key results for the effective triplet lifetime (τ_t = 1.3 μs pre-filling and 1.16 μs post-filling) are stated without accompanying uncertainties, number of measurements, or description of the lifetime extraction method. This is load-bearing for the central claim of achieved purity levels as it prevents quantitative assessment of the improvement and the impact of the nitrogen incursion.
minor comments (3)
  1. The term '5.5 quality' for the starting liquid argon should be defined or referenced to a standard specification for impurity concentrations.
  2. A more detailed schematic or description of the LEGEND Liquid Argon Monitoring Apparatus (LLAMA) would improve clarity on how it detects nitrogen impurities specifically.
  3. Additional references to prior work on LAr purification in other experiments (e.g., DarkSide or MicroBooNE) would contextualize the results better.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive evaluation of our work and the recommendation for minor revision. The single major comment identifies a clear opportunity to strengthen the quantitative presentation of our key purity results, and we will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: The key results for the effective triplet lifetime (τ_t = 1.3 μs pre-filling and 1.16 μs post-filling) are stated without accompanying uncertainties, number of measurements, or description of the lifetime extraction method. This is load-bearing for the central claim of achieved purity levels as it prevents quantitative assessment of the improvement and the impact of the nitrogen incursion.

    Authors: We agree that the submitted manuscript presents the central τ_t values without the supporting details needed for full quantitative assessment. In the revised version we will add: (i) a concise description of the lifetime extraction procedure (fitting the late-time scintillation decay in the three independent monitors), (ii) the number of independent measurements performed before and after filling, and (iii) the combined statistical and systematic uncertainties on each reported τ_t value. These additions will be placed in the sections describing the purity monitors and the filling campaign results, allowing readers to evaluate both the purification improvement and the effect of the residual nitrogen contamination. revision: yes

Circularity Check

0 steps flagged

No significant circularity; results are direct experimental measurements

full rationale

The paper describes the design and performance of a liquid argon purification system for LEGEND-200, reporting empirical measurements of purity via the effective scintillation triplet lifetime τ_t. Starting from 5.5-grade LAr (τ_t ≈ 0.9 μs), the copper-catalyst and molecular-sieve purifier achieved τ_t = 1.3 μs before filling the 91 t cryostat, with a post-filling value of 1.16 μs attributed to a detected nitrogen incursion monitored by LLAMA and other instruments. No equations, parameter fitting, self-referential derivations, or load-bearing self-citations are present; the central claims follow directly from the described engineering sequence, delivery logs, and independent monitor cross-checks without reduction to inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

This is an experimental methods and engineering report. It rests on the standard domain assumption in liquid argon detector technology that scintillation lifetime correlates directly with impurity levels; no free parameters, new entities, or ad hoc axioms are introduced.

axioms (1)
  • domain assumption The effective triplet lifetime τ_t serves as a reliable indicator of liquid argon purity for scintillation-based background discrimination.
    Invoked when using measured τ_t values to quantify achieved purity before and after purification.

pith-pipeline@v0.9.0 · 5757 in / 1519 out tokens · 81862 ms · 2026-05-21T06:49:41.465256+00:00 · methodology

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Reference graph

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