{"id":"acbc7c60-ad5a-4e5b-a09f-d32447a47535","arxiv_id":"2505.01961","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"A pre-study characterizes Li2MoO4 scintillation and heat capacity down to 200 mK and demonstrates a 21.7 g bolometer with 24.6 keV FWHM at 511 keV.","lead":"This paper tests a small lithium molybdate crystal detector at very low temperature and measures its light output, heat capacity, and energy resolution as a first step toward a Chinese neutrinoless double beta decay experiment. The detector works and resolves gamma energies to about 25 keV, but with performance far from what world-leading experiments achieve.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The heat-capacity analysis rejects the linear term in C/T without quantifying it, leaving the mK thermal design input unvalidated; this is the most load-bearing unresolved issue.","rationale":"The reader's weakest assumption, the scintillation extrapolation from 10 K to mK, is real but explicitly acknowledged in Section 2 and affects only the future light-readout design; it does not bear on the demonstrated heat-only bolometer. The missing error bars on the FWHM values are a reporting weakness, but the clear calibration peaks and the admittedly modest resolution still support the conclusion that the bolometer works. The heat-capacity intercept, by contrast, is an internal analysis step used to extract Θ_D and to motivate the mK extrapolation; rejecting it while not quantifying its impact is an unstated assumption in the design foundation. I therefore agree with a CONDITIONAL assessment but for a different reason than the reader's stated weakest assumption. Since the bolometer operation itself is credible and the paper's claims are appropriately qualified, the reader's CONDITIONAL verdict need not change.","tokens_in":7209,"tokens_out":10841,"duration_ms":124385,"concrete_test":"Re-analyze the raw PPMS data with explicit addenda subtraction and report γ, β, and their covariance; then use the assembled 21.7 g bolometer at 28 mK by injecting a known electrical heater pulse into the NTD-Ge and measuring the temperature rise. Compare the inferred C(28 mK) with the Debye-only prediction from Section 3. If the inferred value differs by more than the propagated γ uncertainty, the rejected intercept is physical and the Section 3 design input must be revised.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The weakest load-bearing condition is in Section 3: the fit C/T = γ + β·T² (Eq. 2) gives a non-zero intercept γ, which the paper rejects as 'systematic uncertainty of the testing platform' without reporting its value, its uncertainty, or the effect of keeping it. The Debye temperature is then extracted from β alone. If γ is a real sample contribution (e.g., two-level systems or addenda), it scales as T while the Debye term scales as T³, so at the 28 mK operating point the linear contribution can dominate the crystal heat capacity even if it is negligible in the 200 mK–2 K measurement window. The paper explicitly says the heat-capacity study is used to design the future bolometer sensitivity, so the validity of the mK extrapolation is load-bearing for that design input. The bolometer demonstration itself is credible and the stated resolution is modest, but the heat-capacity foundation is not established.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper reports a pre-study toward a 100Mo neutrinoless double beta decay experiment in China using Li2MoO4 (LMO) bolometers. The authors characterize the scintillation properties of a SICCAS-grown LMO sample from 300 K down to 10 K, measuring the emission spectrum (peaking at 510 nm at 10 K) and the temperature dependence of the light yield. They measure the specific heat of a 14.3 mg LMO sample over 200 mK–2 K, fit C/T = γ + βT^2, extract a Debye temperature ΘD = (330 ± 3) K, and compare it to an independent literature value. They then design, assemble, and operate a (2 cm)^3 cubic LMO bolometer with NTD-Ge heat readout at 28 mK in a ground-above dilution refrigerator, calibrate it with a 22Na source, and obtain FWHM energy resolutions of 24.6 keV at 511 keV and 32.2 keV at 1274 keV. The paper concludes that these studies lay the foundation for manufacturing bolometers in China and for future double beta decay research at the China Jinping Underground Laboratory.","tokens_in":7394,"tokens_out":5303,"duration_ms":54741,"significance":"If the results hold, the paper provides the first domestic demonstration of an LMO bolometer in China, showing that the full chain—crystal production, assembly, cryogenic operation, and signal processing—works with a measurable energy resolution. The scintillation and heat-capacity data for this specific SICCAS LMO crystal are also useful inputs for the community. The FWHM values are modest compared with CUPID or AMoRE, but the paper explicitly acknowledges this and identifies improvement paths. The main strengths are the reproducible detector construction, the use of a matched-filter analysis (with reference to open software), and the independent cross-check of the Debye temperature against a literature value. However, the heat-capacity analysis leaves an unresolved linear term in C/T that is load-bearing for the mK extrapolation, and the scintillation design is based on a 10 K spectrum extrapolated to mK temperatures; these points currently limit the strength of the conclusions drawn from the characterization studies.","major_comments":[{"comment":"The fit to C/T = γ + βT^2 reports no value for the intercept γ, even though the Debye temperature is derived from β alone and the intercept is rejected as a systematic uncertainty of the testing platform. A real linear term, if present, would scale as T and dominate over the T^3 Debye term at the 28 mK operating point, where the bolometer actually runs. Please report γ with its uncertainty, quantify its contribution relative to βT^2 at 28 mK and at 200 mK, and support the rejection either with a direct measurement (e.g., an addenda-only run or a platform background measurement) or by propagating the resulting systematic uncertainty into the predicted mK heat capacity. The current justification relies on a previous PbWO4 study [19] that involves a different crystal and does not, by itself, establish the platform artifact for LMO.","section":"Section 3, Eq. (2)"},{"comment":"The scintillation emission spectrum is measured only down to 10 K, and the manuscript explicitly states that mK-level measurements cannot be made directly. Since the light detector design—semiconductor band gap and anti-reflective coating thickness—depends on the emission wavelength at the operating temperature, the planned dual-readout bolometer is being designed on an extrapolated trend. Please either provide lower-temperature data or soften the design implications in Sections 2 and 6 to reflect this extrapolation uncertainty. This is not a fatal flaw for the heat-only demonstration reported here, but it is load-bearing for the stated next step of building a light-heat dual-readout detector.","section":"Section 2"}],"minor_comments":[{"comment":"The keyword line reads 'Keyworks'; it should be 'Keywords'.","section":"Abstract/Keywords"},{"comment":"The heading 'LMO based bolometer desigh and assembly' contains a typo: 'desigh' should be 'design'.","section":"Section 4 header"},{"comment":"In the figure label, 'HM=32.2WF keV' appears to be a garbled version of 'FWHM=32.2 keV'; please correct it.","section":"Section 5, Figure 10(b)"},{"comment":"The phrase 'in the near further' near the end of the conclusion should likely read 'in the near future'.","section":"Section 6"},{"comment":"To allow the reader to reproduce the Debye temperature from the fitted β, please state explicitly the values of r (number of atoms per unit cell) and the unit-cell count Ncore for the 14.3 mg LMO sample used in Eq. (1).","section":"Section 3, Eq. (1)"},{"comment":"The residual panel labeled Q appears to show only non-negative values; if the residuals are centered near zero, the vertical axis should extend to negative values so the reader can see the full deviation pattern.","section":"Figure 6"},{"comment":"The energy calibration is based on two gamma lines only; please report the uncertainties of the fitted slope and intercept, and the reduced chi-square or equivalent goodness-of-fit statistic, so the reader can judge the calibration quality.","section":"Section 5, calibration fit"}],"recommendation":"major_revision","confidential_remarks":"The paper is a straightforward detector R&D report, and the bolometer demonstration itself appears credible. The main concern is the unquantified intercept in the heat-capacity fit, which directly affects a design input for the mK bolometer. The authors should be required to add the missing quantification and a concrete justification or systematic treatment. The scintillation extrapolation, while explicitly acknowledged, should be handled with more cautious language in the conclusions."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick read: a solid pre-study, not a breakthrough, and it mostly does what it says. The genuinely new pieces are LMO scintillation spectra down to 10 K (280 nm excitation, 510 nm emission), heat capacity down to 200 mK with Θ_D = (330 ± 3) K, and the first (2 cm)^3 LMO bolometer built and operated in China. Running at 28 mK, it gives 24.6 keV FWHM at 511 keV and 32.2 keV at 1274 keV. Those numbers are not competitive with CUPID-grade detectors, and the authors say so. The value is the end-to-end local demonstration: crystal growth, NTD-Ge readout, mounting, calibration, all working. That is real groundwork for the CJPL program.\n\nData handling is mostly sound. The 22Na calibration is straightforward, the matched-filter analysis is standard, and the comparison of the Debye temperature with an independent measurement [20] is a good check.\n\nSoft spots, in order.\n\nFirst, the heat-capacity intercept. The fit C/T = γ + βT² gives a non-zero γ, which the authors reject as testing-platform systematics in one sentence, citing their PbWO4 study [19]. No value, no uncertainty, no effect of keeping it. The stress-test note is right: this is load-bearing, because γT goes linearly in T while the Debye term goes as T³, so even a modest γ can dominate the crystal heat capacity at 28 mK while being buried in the 0.2–2 K fit window. The bolometer demonstration does not depend on this, but the paper says the heat-capacity result is an input to future sensitivity design, and that input is not validated.\n\nSecond, scintillation data end at 10 K. The authors honestly state that mK-level spectra cannot be measured directly, so they extrapolate trends. Since the future light-detector design depends on the emission spectrum, this proxy should carry an explicit uncertainty; right now it reads as a qualitative tendency.\n\nThird, the headline FWHM values have no error bars, and the 10-hour spectrum is low statistics. Minor for a pre-study, but worth adding if this goes to a journal.\n\nThe one self-citation [19] does heavy lifting in rejecting the intercept. PbWO4 platform systematics do not directly constrain LMO sample addenda, so I would ask the authors to quantify γ rather than lean on the analogy.\n\nBottom line: this should go to peer review, not be desk-rejected. It is the right kind of R&D report for JINST or NIM A, with new local data and clearly framed limitations. A referee can request the γ quantification and the FWHM error bars without much trouble. I would bring it to a reading group as a compact example of how pre-studies anchor a bolometer program.","headline":"Solid pre-study of a Chinese LMO bolometer: credible first demonstration and useful low-temperature data, with an unquantified heat-capacity intercept and an acknowledged 10 K-to-mK scintillation extrapolation as the soft spots to fix.","tokens_in":7973,"tokens_out":4829,"would_cite":true,"duration_ms":49105,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A (2 cm)^3 Li2MoO4 bolometer operated at 28 mK with heat-only readout achieves 24.6 keV resolution at 511 keV, establishing a working prototype for a 100Mo neutrinoless double beta decay experiment in China.","keywords":["neutrinoless double beta decay","lithium molybdate (Li2MoO4)","cryogenic phonon scintillating bolometer","scintillation light yield","emission spectrum","low-temperature heat capacity","NTD-Ge readout","100Mo"],"falsifier":"A direct mK-temperature scintillation measurement would settle it: cool an LMO crystal from the same growth line below 50 mK in a dilution refrigerator and record its emission spectrum and light yield with a photodetector covering 350 to 850 nm. If the emission peak departs from 510 nm or the light yield stops increasing below 10 K, the extrapolated design basis for the light-heat dual-readout upgrade fails.","tokens_in":7029,"feed_emoji":"⚛️","tokens_out":18250,"duration_ms":165352,"temperature":0.7,"pith_summary":"This pre-study seeks to establish that lithium molybdate (Li2MoO4, LMO) bolometers can be fabricated and operated in China as detectors for the neutrinoless double $\\beta$ decay of 100Mo. The authors characterise LMO crystals from room temperature down to 10 K, finding the emission spectrum peaks near 510 nm and the light yield rises steeply as temperature drops, and they measure the heat capacity down to 200 mK, obtaining a characteristic temperature $\\Theta_D = (330 \\pm 3)$ K. They then assemble a (2 cm)^3 LMO bolometer read out by a neutron-transmutation-doped germanium thermometer and operate it at 28 mK, reaching an energy resolution of 24.6 keV at 511 keV and 32.2 keV at 1274 keV. These numbers demonstrate working detector operation, and the material data are meant to support a future light-heat dual-readout detector for a deep-underground 100Mo experiment in China.","feed_headline":"China-built LMO bolometer resolves 511 keV at 24.6 keV","feed_subtitle":"A 2-cm-cube heat-only bolometer shows working performance for a planned 100Mo neutrinoless double-beta decay search in China.","key_machinery":"The load-bearing object is the cryogenic phonon scintillating bolometer in its heat-only incarnation: a polished LMO absorber linked to a copper frame through PTFE pieces, with an NTD-Ge resistance thermometer coupled to the crystal and thin gold wire bonds carrying the signal. An energy deposit heats the crystal; the weak thermal link lets it cool back with a decay time of about 30 ms, and a matched optimal filter extracts pulse amplitudes from a triggerless 10 kHz stream. The second mechanism is the $T^{3}$ heat-capacity law with characteristic temperature $\\Theta_D = (330 \\pm 3)$ K, which turns the measured temperature rise into an energy scale and predicts the sensitivity of larger absorbers. The scintillation data are the third piece: the 510 nm emission peak and the low-temperature light-yield growth are the quantitative inputs for designing the future light detector and for enabling $\\alpha$/$\\beta$ discrimination.","core_discovery":"The discovery claimed is that a heat-only LMO bolometer with a cubic (2 cm)^3 absorber can be built and operated at 28 mK on a ground-level cryostat to give clean gamma spectra: the 22Na lines at 511 and 1274 keV are resolved with FWHM 24.6 keV and 32.2 keV, and the Compton edge at 1061 keV plus a 1460 keV 40K line are visible in ten hours of data. On the material side, the paper claims that LMO emission peaks near 510 nm at low temperature and its light yield increases as the temperature falls, especially below 50 K, and that heat capacity follows the $T^{3}$ heat-capacity law with characteristic temperature $\\Theta_D = (330 \\pm 3)$ K down to 200 mK. The authors take the combination as a foundation for a light-heat dual-readout bolometer: the 510 nm peak sets the design target for a light detector and its anti-reflection coating, while the measured heat capacity lets future crystals be designed from the $T^{3}$ heat-capacity law.","pith_inferences":["If the 10 K scintillation trends persist to 28 mK, the dual-readout design should add the alpha/beta discrimination that a single heat channel cannot provide, and the quoted resolutions are then a floor for the full detector.","The heat-capacity measurement together with the observed 29.8 ms decay time is enough to estimate the thermal conductance of the PTFE suspension; a future analysis could check whether that conductance matches the design and whether it contributes thermal noise to the resolution.","A decisive next step would be to move the same bolometer underground: if the background lines shrink while the gamma-peak widths stay fixed, the ground-level resolution loss is environmental, whereas unchanged widths would point to the crystal or readout chain."],"forward_implications":["The demonstrated 24.6 keV FWHM at 511 keV gives a working domestic LMO bolometer as a starting point for the planned 100Mo search.","Using the characteristic temperature $\\Theta_D = (330 \\pm 3)$ K, future LMO crystal sizes and operating temperatures can be chosen with a quantitative prediction of heat capacity and pulse height.","The 510 nm emission peak and the steep light-yield rise below 50 K indicate that a light detector sensitive near 510 nm should provide the light signal needed for alpha/beta discrimination in the dual-readout upgrade.","Longer data taking, better shielding, and operation at the proposed 2400 m underground site should reduce the observed environmental background lines and improve the resolution beyond the ground-level values.","The presence of the 1061 keV Compton edge and the 1460 keV line in ten hours of data shows the detector already has enough spectral quality for calibration and background studies."],"supporting_citations":[{"why":"Defines the cryogenic phonon scintillating bolometer principle that the LMO detector implements.","marker":"[4]"},{"why":"Motivates 100Mo-containing molybdate crystals as absorbers for high-sensitivity neutrinoless double-beta-decay searches.","marker":"[5]"},{"why":"Supplies the Q-value and natural abundance of 100Mo that make it the decay candidate under study.","marker":"[6]"},{"why":"Provides the performance baseline of an existing molybdate bolometer experiment to which the authors compare their resolution.","marker":"[7]"},{"why":"Describes the rock overburden of the proposed deep underground site for the future LMO experiment.","marker":"[13]"},{"why":"Supplies the T^3 heat-capacity law used to fit the data and extract the characteristic temperature.","marker":"[16]"},{"why":"Describes the heat-capacity measurement procedure applied to the LMO sample.","marker":"[19]"},{"why":"Provides earlier heat-capacity data for Li2MoO4 that the measured characteristic temperature is checked against.","marker":"[20]"},{"why":"Documents the electrical and thermal properties of the NTD-Ge sensor used for the heat readout.","marker":"[21]"},{"why":"Supplies the offline analysis software with matched-filter pulse processing used for calibration and resolution extraction.","marker":"[22]"}],"fun_headline_variants":["LMO bolometer resolves 511 keV at 24.6 keV FWHM","Chinese-built LMO bolometer hits 24.6 keV energy resolution","Cubic LMO bolometer achieves 24.6 keV FWHM at 511 keV","LMO bolometer for 100Mo decay shows 24.6 keV resolution","China's LMO bolometer: 24.6 keV FWHM on 511 keV line"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the scintillation properties measured only down to 10 K—emission peaking near 510 nm and light yield rising steeply at low temperature—remain representative down to the 28 mK bolometer operating temperature, since no direct mK scintillation measurement was made.","fun_headline_variants_meta":{"raw":{"variants":["LMO bolometer resolves 511 keV at 24.6 keV FWHM","Chinese-built LMO bolometer hits 24.6 keV energy resolution","Cubic LMO bolometer achieves 24.6 keV FWHM at 511 keV","LMO bolometer for 100Mo decay shows 24.6 keV resolution","China's LMO bolometer: 24.6 keV FWHM on 511 keV line"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000966,"raw_usage":{"total_tokens":4118,"prompt_tokens":958,"completion_tokens":3160,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":574,"completion_tokens_details":{"reasoning_tokens":3048}},"tokens_in":574,"tokens_out":3160,"duration_ms":23041,"temperature":1.0,"reasoning_tokens":3048,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T04:04:29.312487+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A direct mK-temperature scintillation measurement would settle it: cool an LMO crystal from the same growth line below 50 mK in a dilution refrigerator and record its emission spectrum and light yield with a photodetector covering 350 to 850 nm. If the emission peak departs from 510 nm or the light yield stops increasing below 10 K, the extrapolated design basis for the light-heat dual-readout upgrade fails.","supporting_citations":[{"cited_title":"Scintillating bolometers for double beta decay search,","cited_arxiv_id":null,"evidence_quote":"Defines the cryogenic phonon scintillating bolometer principle that the LMO detector implements."},{"cited_title":"Development of 100Mo-containing scintillating bolometers for a high- sensitivity neutrinoless double-beta decay search,","cited_arxiv_id":null,"evidence_quote":"Motivates 100Mo-containing molybdate crystals as absorbers for high-sensitivity neutrinoless double-beta-decay searches."},{"cited_title":"Q values of the 76Ge and 100Mo double-beta decays,","cited_arxiv_id":null,"evidence_quote":"Supplies the Q-value and natural abundance of 100Mo that make it the decay candidate under study."},{"cited_title":"In situ observation of rock spalling in the deep tunnels of the China Jinping Underground Laboratory (2400 m depth),","cited_arxiv_id":null,"evidence_quote":"Describes the rock overburden of the proposed deep underground site for the future LMO experiment."},{"cited_title":"Physics behind the Debye temperature","cited_arxiv_id":"physics/0703001","evidence_quote":"Supplies the T^3 heat-capacity law used to fit the data and extract the characteristic temperature."},{"cited_title":"Study of a coherent elastic neutrino-nucleus scattering experiment at a reactor with a PbWO 4-based bolometer,","cited_arxiv_id":null,"evidence_quote":"Describes the heat-capacity measurement procedure applied to the LMO sample."},{"cited_title":"Offline data processing software for a Li 2MoO4 bolometer demon- stration experiment at China Jinping Underground Laboratory,","cited_arxiv_id":null,"evidence_quote":"Supplies the offline analysis software with matched-filter pulse processing used for calibration and resolution extraction."}],"review_version":1}