{"id":"bdf8f165-c35a-4ecd-8abf-662ac27273ce","arxiv_id":"2411.17934","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"A tonne-scale liquid argon detector instrumented with 4 m^2 of PEN wavelength-shifting reflector shows no light-yield deterioration over 12 days.","lead":"This paper tests whether PEN plastic foils, a cheaper and easier alternative to the standard TPB coating, keep working in a large liquid argon detector. After 12 days of running a two-tonne detector with 4 square meters of PEN, the light output stayed stable, suggesting PEN could be practical for future massive argon detectors.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 12-day stability claim rests on attributing the 2.3±1.2%/day light-yield decline during days 8–11 to impurity buildup rather than PEN degradation, but no independent impurity measurement or controlled PEN test is provided.","rationale":"I agree with the reader's CONDITIONAL verdict. The stability claim is the paper's central contribution, and it is genuinely supported by the flat slopes on days 12–19 and the internal consistency between alpha and muon data. However, the 12-day claim cannot be sustained if the days 8–11 decline is real PEN deterioration. The paper does not provide an independent measurement that would distinguish between the two explanations; the stable triplet lifetime only eliminates one class of impurity (triplet quenchers) and is consistent with VUV-absorbing impurities, so the ambiguity is real. The proposed bench test would settle the question directly by measuring PEN's intrinsic response to the relevant VUV dose. Thus the verdict remains CONDITIONAL pending such a test, and no change to the reader's assessment is needed. The paper deserves credit for clearly acknowledging the ambiguity and for reporting the stable days 12–19 window, but the central claim still depends on an untested attribution.","tokens_in":8933,"tokens_out":7591,"duration_ms":65755,"concrete_test":"Expose identically manufactured Teonex Q53 PEN samples to the same integrated 128 nm VUV fluence as received by the 4 m² foils during the 12-day run (the paper estimates this corresponds to 1–3 years of underground operation), and measure their WLS conversion efficiency relative to TPB before and after exposure. If the efficiency is unchanged within ~1%, the days 8–11 decline cannot be attributed to PEN degradation, supporting the stability claim. If the efficiency drops at a rate comparable to 2.3±1.2%/day, the stability claim fails.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's headline claim—'no evidence of performance deterioration over a period of 12 days'—rests on interpreting the 2.3±1.2%/day decline in muon light yield observed between days 8–11 as impurity buildup rather than PEN degradation. The text itself acknowledges this: 'If we assume that the decline is entirely due to PEN degradation, a linear fit estimates LY loss of 2.3±1.2% per day.' No independent impurity concentration or VUV-transparency measurement is reported. The triplet lifetime is stable over the same period (≈1.38–1.44 μs), which rules out triplet-quenching impurities but not VUV-absorbing impurities; it also does not exclude PEN damage. The stable phase (days 12–19, after excluding days 15–16 as noisy) is only 8 days long. If the impurity assumption is wrong, the days 8–11 data directly contradict the stability claim. The paper is transparent about this ambiguity, but the central conclusion requires a resolution that the presented data cannot provide.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a test of a 4 m^2 PEN-based wavelength-shifting reflector installed in a two-tonne liquid argon dewar at CERN. The light yield from 241Am alpha particles and cosmic-ray muons is tracked over roughly 17 days of operation, with a triplet-lifetime correction applied to the daily light yield. The authors report a stable light yield between days 12 and 19 and interpret a decline seen between days 8 and 11 as impurity buildup, while acknowledging that it could be PEN degradation. The paper concludes that PEN shows no evidence of performance deterioration over a period of 12 days and is therefore a viable substitute for TPB in large-scale liquid argon detectors.","tokens_in":9146,"tokens_out":9782,"duration_ms":81229,"significance":"If the stability claim holds, this is an important step toward using PEN as a large-area wavelength shifter in future liquid argon detectors, since PEN is substantially easier to instrument than TPB. The paper is the first to test a 4 m^2 PEN reflector over many days in a tonne-scale detector, and it uses two independent event classes (alpha particles and cosmic-ray muons) to cross-check the light yield. The authors are transparent about systematic uncertainties and the ambiguity in the days 8-11 decline. However, the central claim as stated is not fully supported: the stable window is only eight days long with two days excluded, and the attribution of the days 8-11 decline to impurities is not backed by an independent measurement. The paper is a valuable first large-scale stability study, but the conclusion needs to be tempered or supported with additional evidence.","major_comments":[{"comment":"The abstract claims \"no evidence of performance deterioration over a period of 12 days,\" but the quantitative support in Section 5 is limited to eight days (days 12-19), and the same 12-day window includes days 8-11, for which the paper reports a decline of 2.3±1.2% per day if interpreted as PEN degradation. The claim as stated is therefore not supported by the data as presented; the authors should either restrict the claim to the stable eight-day window or provide an independent impurity measurement that removes the ambiguity of the days 8-11 decline.","section":"Abstract and Section 5"},{"comment":"The attribution of the days 8-11 light-yield decline to impurity buildup is not supported by any direct measurement. The triplet lifetime is stable over the same period (1.38-1.44 μs), which excludes triplet-quenching impurities but not VUV-absorbing impurities or PEN degradation. No independent impurity concentration, VUV-transparency measurement, or controlled exposure test is reported. Given that the paper explicitly states that a linear fit yields 2.3±1.2% per day loss under the PEN-degradation interpretation, the central stability conclusion requires resolving this ambiguity; the presented data cannot distinguish the two hypotheses.","section":"Section 5, second paragraph"},{"comment":"The triplet-lifetime correction factor η_i = (F_prompt + (1−F_prompt)·τ_0/τ_i) defined in Section 4.1 accounts only for impurities that take energy from triplet excimers, i.e., reduce the triplet lifetime. It does not correct for VUV-absorbing impurities, which reduce the light yield without changing the observed triplet lifetime. In Section 5, the days 8-11 decline is attributed to \"impurities that absorb VUV light,\" a mechanism that is outside the scope of the applied correction. The paper should either justify why the triplet-lifetime correction is applicable to all impurity effects or provide an independent basis for the VUV-absorption scenario.","section":"Section 4.1 and Section 5"},{"comment":"The stability conclusion rests on the eight-day window from days 12 to 19, from which two days (15 and 16) are excluded because of \"a sudden unexplained high rate of correlated noise\" that caused an \"apparent increase\" in the light yield. Excluding a quarter of the already short stable window without a demonstrated instrumental cause weakens the evidentiary basis for the stability claim. The authors should provide additional information about the noise event and, if possible, reanalyze the full window or justify the exclusion with an instrumental diagnostic.","section":"Section 4.1 and Figure 5 (left)"}],"minor_comments":[{"comment":"The paper reports a 1% per day downward drift in the mean single-photoelectron charge but does not describe how this drift is corrected in the light-yield values. Figure 5 (left) distinguishes \"µ events\" from \"µ events (without PMT calibration)\"; please clarify which data are gain-corrected and how the correction was applied.","section":"Section 3"},{"comment":"The absolute PEN efficiency (ε_PEN=0.45 for center, 0.55 for edge) and the VUV absorption length (60 cm) are obtained by matching the simulation to the data, and these values are then used to compute the \"Model expectation\" bands in Fig. 5 (right). The authors should state explicitly that this is a fit to the same data and provide uncertainties on the extracted parameters, or present the comparison as a consistency check rather than a prediction.","section":"Section 4.2"},{"comment":"The bracket notation indicating data taken with the oscilloscope is not defined in the caption; please add an explicit note in the caption or in the text.","section":"Figure 5 (left) caption"},{"comment":"The statement that the VUV exposure over the measurement period is equivalent to 1-3 years of operation in a deep-underground detector is asserted without a derivation or uncertainty estimate; given that the degradation mechanism is not established, this equivalence should be presented as a rough scaling estimate with its assumptions stated.","section":"Section 5, first paragraph"},{"comment":"The extracted text contains many concatenated words (e.g., in the abstract) that appear to be a conversion artifact; please ensure the published version has proper spacing.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is within scope for JINST as an instrumentation paper, and the experimental effort is significant. The main concern is that the headline stability claim overstates the evidence: the 12-day statement in the abstract is not supported by the eight-day stable window and the unresolved days 8-11 decline. The authors should either add an independent impurity measurement (e.g., a purity monitor) or rephrase the claim to refer only to the stable window. The circularity in the absolute efficiency is secondary since the stability claim is relative, but it should be acknowledged more explicitly."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a genuinely useful first tonne-scale dataset on PEN as a wavelength shifter in liquid argon, but the headline \"no evidence of performance deterioration over a period of 12 days\" overstates what the data support. The stable window is really days 12–19 (8 days), with days 15–16 excluded for unexplained correlated noise, and the earlier days 8–11 show a decline that the authors attribute to impurity buildup without direct evidence. The paper is transparent about that attribution, so nothing is hidden, but the central claim is conditional.\n\nWhat is new and good: previous PEN measurements used samples under 0.04 m^2 and none reported explicit stability results. This paper uses 4 m^2 of PEN/reflector foil in a two-tonne dewar, tracks both alpha and cosmic muon light yield, includes source position scans for uniformity, and applies a triplet-lifetime correction for impurity effects. The 8-day stable window shows slopes consistent with zero for both alpha and muon data, and the agreement between alpha and muon yields supports a uniform response across the foil. That is a real engineering qualification step.\n\nThe soft spots are real but proportionate. The days 8–11 decline is the main one: the triplet lifetime is stable over that period, which rules out triplet-quenching impurities but not VUV-absorbing ones, and the paper itself notes that if the decline were entirely PEN degradation it would be 2.3 ± 1.2% per day. Without an independent impurity measurement or a controlled PEN test, you cannot cleanly separate degradation from contamination. Separately, the absolute PEN efficiency extraction has some circularity — simulation is matched to the data and then used as the expectation — and the VUV absorption length is also chosen to fit the data. But the stability claim is relative and does not depend on that fit. Excluding days 15–16 is reasonable, though it shortens the already short stable window.\n\nWho this is for: people working on photon detection for DarkSide-20k, DUNE, or other large LAr detectors. It is a useful dataset with an honest discussion of limitations. I would send it to peer review; it deserves referee time, with the expectation that the authors clarify the impurity attribution and present the stable window as 8 days rather than 12. I would cite it in my own work on PEN WLS.","headline":"First tonne-scale PEN stability test in LAr, but the 12-day claim really rests on an 8-day window and an unverified impurity assumption.","tokens_in":9822,"tokens_out":1674,"would_cite":true,"duration_ms":16388,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["29.40.Mc"],"model":"deepseek-v4-flash","headline":"A 4 m² PEN-based wavelength-shifting reflector in a two-tonne liquid argon detector shows no evidence of performance deterioration over 12 days, making PEN a viable substitute for the standard TPB coating.","keywords":["wavelength shifters","polyethylene naphthalate","PEN","liquid argon detectors","light yield stability","TPB replacement","scintillation detection","detector instrumentation"],"falsifier":"Run the same large PEN reflector in a liquid argon detector with active purification and continuous impurity monitoring, so that the impurity level is known and held constant; if the days-8-11 decline rate of about 2.3% per day still appears, then the stability claim is falsified. A more direct test would be to expose a PEN sample to a controlled VUV flux while measuring its conversion efficiency in situ, with no other variables changing.","tokens_in":8674,"feed_emoji":"⚛️","tokens_out":6305,"duration_ms":51336,"temperature":0.7,"pith_summary":"Liquid argon detectors need a wavelength shifter to convert 128 nm scintillation light into visible light, and the current standard TPB is hard to apply over the huge surfaces of next-generation detectors. This paper tests a 4 m² reflector made of commercial PEN film, which can be produced as thin sheets, inside a two-tonne liquid argon detector over about two weeks. Tracking light yield with alpha particles and cosmic-ray muons, it sees no evidence of performance deterioration over 12 days of data after correcting for impurity effects. If the result holds, PEN becomes a viable, much easier-to-install substitute for TPB in large liquid argon detectors.","feed_headline":"PEN foil holds light yield steady for 12 days in liquid argon","feed_subtitle":"A cheap plastic sheet could replace the hard-to-coat standard wavelength shifter in giant argon detectors.","key_machinery":"The central object is the PEN-based wavelength-shifting reflector (WLSR): a 25 µm sheet of commercial PEN backed by a specular reflector, mounted on the inner surface of a hexagonal cage inside the liquid argon. PEN converts argon scintillation VUV photons to visible light near 430 nm. The stability measurement works by tracking the daily light yield from two independent probes, 4.8 MeV alpha particles and cosmic-ray muons, and by applying a correction based on the measured triplet lifetime of argon to separate the effect of accumulating impurities from any true change in the PEN response.","core_discovery":"The paper claims that a PEN-based wavelength-shifting reflector covering 4 m² of a tonne-scale liquid argon detector maintains a stable light yield over 12 days, with a fitted slope consistent with zero for both alpha and muon signals in the main dataset. It also reports that the light yield is uniform across the reflective cage volume, and that the inferred PEN conversion efficiency is around 45% relative to TPB, consistent with earlier small-sample measurements. The authors interpret the one declining segment of data as impurity buildup rather than PEN degradation, on the grounds that the degradation-only interpretation would imply a light-yield loss of 2.3±1.2% per day.","pith_inferences":["The key uncertainty is whether impurity buildup truly explains the days 8–11 decline; a direct measurement of argon purity during the run would settle that, and the authors do not provide one.","The claimed equivalence between the test's VUV exposure and 1–3 years underground assumes VUV dose is the only degradation mechanism; other stressors such as temperature cycling, humidity, or chemical exposure could shorten PEN's usable lifetime in real detectors.","A natural next step is a head-to-head comparison of PEN and TPB in the same tonne-scale setup over months, which would quantify both the efficiency gap and any difference in long-term stability.","If PEN stability holds, the ease of manufacturing large sheets could reshape how photon detection systems are built, moving wavelength shifting from a deposited coating to a structural cladding."],"forward_implications":["Next-generation liquid argon detectors could cover their large surfaces with PEN foils instead of vacuum-deposited TPB, greatly simplifying instrumentation.","The paper equates the VUV exposure during the 12-day test to 1–3 years of operation in a deep underground rare-event search detector, implying the stability extends to those exposures if VUV dose is the main degradation driver.","The agreement between alpha- and muon-measured light yields indicates that the PEN response is uniform over the full cage volume, not just near the source.","The measured PEN efficiency of about 45% relative to TPB is consistent with small-sample results, so upscaling to tonne scale appears not to introduce an efficiency penalty."],"supporting_citations":[{"why":"Supplies the prior direct comparison of PEN and TPB in liquid argon, including the 47% relative efficiency that motivates the large-scale test.","marker":"[16]"},{"why":"Characterizes the quantum efficiency of PEN and TPB and the reflector behavior that the setup's foil choice is based on.","marker":"[17]"},{"why":"Establishes PEN film as a wavelength shifter for liquid argon detectors in the first place.","marker":"[15]"},{"why":"Provides earlier measurements of PEN wavelength-shifting performance in liquid argon that the efficiency comparison relies on.","marker":"[20]"},{"why":"Reports the only previous multi-day PEN measurement and the lack of explicit stability results, defining the gap this paper fills.","marker":"[21]"},{"why":"Supplies the photomultiplier tube characterization and quantum efficiency used for the light-yield calibration.","marker":"[24]"},{"why":"Documents how nitrogen and oxygen contamination reduce liquid argon light yield, motivating the triplet-lifetime correction used to separate impurity effects from PEN degradation.","marker":"[38]"}],"fun_headline_variants":["PEN reflector holds steady for 12 days in liquid argon","Cheap plastic PEN passes 12-day argon stability test","PEN films keep tonne-scale argon detector light stable","No decay in 12 days: PEN reflector for argon detectors"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The conclusion depends on assuming that the light-yield decline seen in the second dataset (days 8–11) was caused by impurity buildup rather than by PEN itself deteriorating, without an independent impurity measurement to back that up.","fun_headline_variants_meta":{"raw":{"variants":["PEN reflector holds steady for 12 days in liquid argon","Cheap plastic PEN passes 12-day argon stability test","PEN films keep tonne-scale argon detector light stable","No decay in 12 days: PEN reflector for argon detectors"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000222,"raw_usage":{"total_tokens":1408,"prompt_tokens":855,"completion_tokens":553,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":471,"completion_tokens_details":{"reasoning_tokens":485}},"tokens_in":471,"tokens_out":553,"duration_ms":5115,"temperature":1.0,"reasoning_tokens":485,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T11:40:26.610703+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same large PEN reflector in a liquid argon detector with active purification and continuous impurity monitoring, so that the impurity level is known and held constant; if the days-8-11 decline rate of about 2.3% per day still appears, then the stability claim is falsified. A more direct test would be to expose a PEN sample to a controlled VUV flux while measuring its conversion efficiency in situ, with no other variables changing.","supporting_citations":[{"cited_title":"Kuźniak, B","cited_arxiv_id":null,"evidence_quote":"Establishes PEN film as a wavelength shifter for liquid argon detectors in the first place."},{"cited_title":"Wavelength-Shifting Performance of Polyethylene Naphthalate Films in a Liquid Argon Environment","cited_arxiv_id":"2103.03232","evidence_quote":"Provides earlier measurements of PEN wavelength-shifting performance in liquid argon that the efficiency comparison relies on."},{"cited_title":"Abed Abud, B","cited_arxiv_id":null,"evidence_quote":"Reports the only previous multi-day PEN measurement and the lack of explicit stability results, defining the gap this paper fills."},{"cited_title":"Test and characterization of 400 Hamamatsu R5912-MOD photomultiplier tubes for the ICARUS T600 detector","cited_arxiv_id":"1807.08577","evidence_quote":"Supplies the photomultiplier tube characterization and quantum efficiency used for the light-yield calibration."},{"cited_title":"Effects of Nitrogen and Oxygen contamination in liquid Argon.Nucl","cited_arxiv_id":null,"evidence_quote":"Documents how nitrogen and oxygen contamination reduce liquid argon light yield, motivating the triplet-lifetime correction used to separate impurity effects from PEN degradation."}],"review_version":1}