{"id":"24a639a5-2631-4b5f-ba33-0bac8d1997e2","arxiv_id":"2607.13726","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"A commercial 2 mm pixelated silicon detector achieves about 3-4 keV resolution and high linearity for electron spectroscopy, but percent-level charge sharing must be mitigated before it meets PERC's precision goals.","lead":"This paper tests a commercially built 2-mm-thick silicon detector for measuring electrons from neutron decay, a key signal for precision tests of the weak force. The detector shows good energy resolution and stability, but energy can be split between neighbouring pixels at the percent level, which the authors say needs more work before the detector can serve PERC's precision goals.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 1e-4-level electron energy response is not established: the photon-anchored linear calibration is extrapolated to the full beta spectrum, and the single 975 keV electron validation point leaves a ~1.2 keV residual that is not propagated into the quoted systematic uncertainty.","rationale":"The paper is careful and honest: it openly states the calibration range limitation (section 4.4), reports per-pixel results, and flags charge sharing/cross-talk as 'highly significant effects... require further studies' (section 4.7). The measurements themselves (leakage current, stability, resolution, dead layer) appear internally consistent and are not in question. The load-bearing gap is the transfer from photon calibration to the electron energy scale over the full beta spectrum. The claimed systematic calibration uncertainty 2-8e-4 and 'below 100 eV' refer to photon fits; the electron validation is a single point with a keV-level residual. For a Fierz-term measurement at Delta b=1e-3, the response must be known to ~1e-4; a residual 1.3e-3 would dominate. This is not an external-consensus dispute; it is an internal gap between the evidence reported and the suitability conclusion. The reader's weakest assumption identifies exactly this, so I agree. A concrete re-fit of the 207Bi spectra can test both differential linearity and the absolute air-loss scale. Because the paper already qualifies the suitability as requiring further studies, the CONDITIONAL verdict stands; no new verdict category is needed.","tokens_in":14650,"tokens_out":7944,"duration_ms":89298,"concrete_test":"Re-analyze the existing 207Bi electron data with the K-, L-, M-line energies free (rather than fixed) and with the air-loss correction as a free parameter. If the measured K-L spacing deviates from 72.144 keV by more than 0.2 keV, the linearity extrapolation is invalid; if the best-fit air-loss must differ from 4.3 keV by ~1.3 keV to align with the photon calibration, the absolute electron energy scale carries an unquantified systematic that must be added to the uncertainty budget.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The suitability claim for PERC (Delta b = 1e-3) requires an energy-response calibration at the ~1e-4 level over 0-782 keV. Section 4.4 calibrates with photon lines up to 661 keV, explicitly states the calibration function 'was assumed to be linear,' and concedes the full range up to 1 MeV could not be covered. The only electron validation is the 207Bi K conversion line (section 4.6): measured at 970.1(1) keV while the simulation-corrected expectation is ~971.4 keV (975.651 keV minus 4.3 keV air loss), a ~1.3 keV residual. This residual is called 'reasonable agreement,' but it is 1.3e-3 relative — more than an order of magnitude above the 1e-4-level goal — and the systematic uncertainty quoted in section 4.4 (2-8e-4) is derived from photon fits that do not include this electron-scale offset, the uncertainty in the 4.3 keV air-loss correction (which has no quoted uncertainty), or the incomplete electron response model (section 4.6 notes 'the fit function needs further refinement'). Until this residual is understood and propagated, the linearity extrapolation and the resulting electron energy scale are not established at the level required for the Fierz-term projection.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript characterises a commercially available 2 mm thick pixelated silicon PIN detector (MSPX128) for use in electron spectroscopy of neutron beta decay in the PERC experiment. Measurements at room temperature cover leakage current, long-term stability, electronic noise, photon-energy calibration using 133Ba and 137Cs lines, signal rise time, electron response using 207Bi conversion electrons, charge sharing between pixels, and dead-layer thickness. The authors report good energy resolution (about 3.1 keV for photons, 4 keV for electrons), low drift, linear calibration with fractional systematic uncertainty 2–8e-4, and a dead layer of 123(6) nm. They conclude the detector is a viable upgrade for PERC but note that charge sharing/cross-talk at the percent level requires further study.","tokens_in":14864,"tokens_out":2702,"duration_ms":29339,"significance":"If the characterisation is trustworthy, this is a useful contribution to the development of precision beta-spectroscopy detectors. The measurements are careful and internally consistent: leakage currents are below 20 nA, drift is below 0.15 eV/h, and the simultaneous photon calibration with reduced chi-square 1.1–1.3 is well executed. The paper also provides an openly described analysis and cites external benchmark energies, so the calibration is not circular. The main significance is the quantitative assessment of whether a room-temperature, commercial silicon pixel detector can meet the 1e-4-level energy response required for the PERC Fierz-term goal. However, the current evidence is incomplete: the electron validation is limited to one conversion-electron point, the photon calibration range stops at 661 keV, and the charge-sharing effect is percent-level. Thus the paper supports the detector's potential but does not yet establish the full suitability claim.","major_comments":[{"comment":"The Summary states 'calibration uncertainty below 100 eV,' but §4.4 quotes a conservative fractional systematic uncertainty of 2...8×10^-4. At 782 keV, 8×10^-4 corresponds to about 0.6 keV, and at 1 MeV about 0.8 keV—far above 100 eV. Please reconcile the two statements and specify the energy at which the sub-100 eV claim applies.","section":"§4.4 and §5"},{"comment":"The only electron validation point is the 207Bi K conversion line: measured at 970.1(1) keV against a simulation-corrected expectation of ~971.4 keV (975.651 keV minus 4.3 keV air loss). The ~1.3 keV residual is roughly 1.3×10^-3 relative, more than an order of magnitude above the 1e-4 goal. The text calls this 'reasonable agreement' without assigning an uncertainty to the 4.3 keV air-loss correction or the response model. This residual and its uncertainty must be propagated into the quoted systematic error budget before the 1e-4-level electron response can be claimed.","section":"§4.6"},{"comment":"The calibration function is assumed linear and anchored on photon lines up to 661 keV plus a single 975 keV electron point. The text explicitly states the full range up to 1 MeV could not be covered. A nonlinearity between 661 keV and 782 keV, or a difference between photon and electron response, would directly affect the beta-spectrum calibration. The authors should either provide an upper bound on such nonlinearity from the electron residual or restrict the claim of 'highly linear' to the calibrated photon range.","section":"§4.4, §4.6"},{"comment":"Charge-sharing/cross-talk is found to affect about 31% of 975 keV electron events, with measured energy shifts of 6.8 keV and 14.8 keV for two- and three-pixel shared events. These effects are percent-level, far larger than the 1e-4 goal, and are not included in the electron calibration or the systematic uncertainty. The paper itself concludes 'requires further studies.' For the PERC Fierz-term projection, this is a load-bearing gap: the energy scale for electrons that experience charge sharing is not yet calibrated at the required level.","section":"§4.7"}],"minor_comments":[{"comment":"The element should be written V_ud (subscript) for clarity.","section":"Abstract"},{"comment":"Typo: 'another another line at 53.1622 keV'—remove the duplicated word.","section":"§4.4"},{"comment":"These figures are credited to [34], an unpublished thesis. The paper should be self-contained; at minimum, describe the key fitting features in the text or include the relevant plots in the main paper.","section":"Figures 6, 7, 10"},{"comment":"The 4.3 keV air-loss correction is quoted without uncertainty. Please estimate and report its uncertainty, since it directly affects the electron validation residual.","section":"§4.6"},{"comment":"The optimal rise time is stated as ~4 µs from the fit, but 3 µs was chosen because it gave the narrowest width across pixels. Please clarify the discrepancy and the reason for the choice.","section":"§4.3"}],"recommendation":"major_revision","confidential_remarks":"The measurement quality is genuinely good, and the paper contains a lot of useful information for the detector community. The main gap is the unquantified electron-response residual and the percent-level charge-sharing effect, both of which directly bear on the suitability claim. These are fixable in a revision, so I recommend major revision rather than rejection. I would also encourage the authors to soften the Summary claim until the electron calibration residual is propagated."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Honest, careful detector characterisation paper that mostly delivers on what it promises, but the headline linearity claim is for photons up to 661 keV, and the electron response at the 1e-4 level is not actually established. That distinction matters for the PERC Fierz-term goal, and the paper would be stronger if it said so more plainly.\n\nWhat's new: room-temperature calibration with commercial electronics up to 661 keV, a linearity check at the 2-8e-4 level, rise-time versus bias voltage compared to PENELOPE simulation, and a direct measurement of charge-sharing/cross-talk with 975 keV conversion electrons. The per-pixel leakage current and 300 h drift data are also solid. The paper is properly hedged — it flags the charge-sharing as 'highly significant effects' needing further study (section 4.7) and admits the calibration does not cover the full range to 1 MeV (section 4.4). That openness earns real credit.\n\nThe soft spots are the ones the stress-test identifies. The calibration fits photon lines up to 661 keV, and the 975 keV electron point sits at 970.1(1) keV against a simulation-corrected expectation of ~971.4 keV. The ~1.2 keV residual is brushed off as 'reasonable agreement,' but it is more than an order of magnitude above the 1e-4 fractional response the PERC Fierz projection needs, and the systematic uncertainty quoted (2-8e-4) is derived from photon fits that do not include this electron-scale offset or the unquoted uncertainty on the 4.3 keV air-loss correction. The linearity extrapolation to the full beta spectrum is load-bearing. This doesn't invalidate the detector characterisation — it means the paper's suitability claim for PERC is not yet proven.\n\nMinor mechanical issues: the DOI in ref [37] is a placeholder ('ksmp-zxsl'), and no data release accompanies the paper while several key figures come from Lebert's unpublished thesis. Those should be fixed in revision.\n\nOverall: this is a solid, useful characterisation for anyone working with thick pixelated silicon detectors or planning PERC-type electron spectroscopy. It deserves a serious referee. My recommendation: send to review, and require the authors to either extend the electron calibration or explicitly restrict the linearity claim to the photon-calibrated range.","headline":"Solid, honest detector characterisation, but the photon linearity claim is stretched when applied to electrons without a proper electron-scale systematic budget.","tokens_in":15522,"tokens_out":2350,"would_cite":true,"duration_ms":24415,"reading_group":"maybe","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 mm thick pixelated silicon detector, run at room temperature with commercial electronics, is shown to be linear and stable enough to serve as the main electron spectrometer for a high-precision neutron beta-decay measurement.","keywords":["silicon detector","pixelated detector","electron spectroscopy","neutron beta decay","energy calibration","charge sharing","energy resolution","dead layer"],"falsifier":"Place an open, thin-foil 207Bi source in vacuum and measure the 975.651 keV K-line together with additional conversion lines down to about 480 keV; if each line's position deviates from a single linear calibration by more than the quoted systematic uncertainty, or if the K-line residual to the simulation-corrected prediction does not reproduce the ~1.2 keV offset, the linearity and calibration-uncertainty claims fail.","tokens_in":14385,"feed_emoji":"🔬","tokens_out":6932,"duration_ms":64563,"temperature":0.7,"pith_summary":"The paper characterises a large-area, 2 mm thick pixelated silicon detector built to record the complete 0–782 keV electron spectrum of free neutron beta decay, in place of the plastic scintillator originally planned for the experiment. It aims to prove that the detector can meet the experiment's demanding calibration goals even at room temperature with commercial readout: a linear energy response with fractional systematic calibration uncertainty of 2–8 parts in 10,000, a photon energy resolution of about 3.1 keV and an electron resolution of about 4 keV, and drift below 0.15 eV/h over 300 h. The motivation is that such a detector would make it possible to measure the beta-asymmetry parameter and the Fierz interference term b (a probe of scalar and tensor currents) with enough precision to constrain the CKM element V_ud and search for new physics. The paper additionally identifies a percent-level charge-sharing and cross-talk effect between pixels that shifts the energy of roughly one third of 975 keV events and calls for further study before the most demanding goals.","feed_headline":"Silicon detector calibration uncertainty drops below 100 eV","feed_subtitle":"Room-temperature 2 mm pixelated detector: drift under 0.15 eV/h, 4 keV electron resolution, ready for precision beta-decay spectroscopy.","key_machinery":"The central object is a 2 mm thick, 117 mm diameter pixelated silicon PIN detector whose entrance side is a continuous boron-doped layer (no insensitive dead region) and whose back side is divided into 127 hexagonal pixels with 100 µm gaps. The argument is carried by a simultaneous linear calibration fit to six photon lines, extended by one 975 keV electron point, together with a noise decomposition of the trapezoidal-filter resolution into parallel, series, and 1/f contributions and a two-/three-pixel coincidence analysis that maps charge sharing and cross-talk. The linear calibration model is the load-bearing identity: everything else—resolution, drift, dead layer, charge sharing—is assess","core_discovery":"Using six photon lines from 133Ba and 137Cs between 80 and 661 keV, the authors perform a simultaneous fit assuming a linear channel-energy relation; a second-order term contributes at the 10^-6 level and per-line fits show no systematic tension, so the detector is declared highly linear. Extending to electrons, the 975.651 keV conversion line of 207Bi is measured at 970.1(1) keV after a simulation-corrected air loss of about 4.3 keV, which the authors call reasonable agreement with the expected ~971.4 keV. The full-depletion voltage is found to be 50–60 V instead of the nominal 300 V, consistent with the doping inferred from capacitance measurements. The characterisation also quantifies cha","pith_inferences":["A natural next test is to calibrate with open, thin-foil conversion-electron sources under vacuum across 0–1 MeV; that would directly decide whether the linearity inferred from photon lines survives in the electron channel.","If the cross-talk shift is indeed caused by femtofarad-level parasitic capacitance, reducing pin-header length or adding shielding between readout channels should shrink the 6.8/14.8 keV shifts and lower the charge-sharing loss fraction.","Event-by-event reconstruction that sums energies of time-correlated neighbouring pixels could convert the charge-sharing 'loss' into a corrected full-energy peak; the paper does not demonstrate this, but the data it presents make the test straightforward.","The factor-of-ten discrepancy between nominal and measured doping suggests production spread; a capacitance-voltage check on each detector unit would be a cheap quality-control gate before deploying a batch."],"forward_implications":["The detector can replace the planned plastic scintillator as the main electron detector, gaining about an order of magnitude in energy resolution (3.1 keV photons, 4 keV electrons) and far better linearity.","Drift below 0.15 eV/h over 300 h means a single calibration can stay valid for long running campaigns.","Fractional systematic calibration uncertainty of 2–8×10^-4 keeps the induced uncertainty on the beta-asymmetry parameter below 10^-4, and meets the O(10^-4) gain precision needed for a Fierz-term precision of 10^-3.","The observed ~31% charge-sharing fraction and cross-talk shifts of 6.8 keV / 14.8 keV are significant for precision beta spectroscopy and require further investigation; this is the main caveat to using the current readout for the Fierz goal.","The 123(6) nm dead layer shifts a 50 keV electron by only about 30 eV, so dead-layer effects are negligible for the electron measurement."],"fun_headline_variants":[],"cache_read_input_tokens":2304,"weakest_assumption_plain":"That a linear energy calibration anchored on photon lines up to 661 keV plus one 975 keV electron point represents the full 0–782 keV electron response at the 10^-4 level; the authors could not cover the full range with an adequate source, and the 970.1(1) keV electron peak sits ~1.2 keV from the simulated expectation, a residual large compared with the goal.","fun_headline_variants_meta":{"error":"'choices'"},"cache_creation_input_tokens":0},"created_at":"2026-08-02T03:55:08.204054+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Place an open, thin-foil 207Bi source in vacuum and measure the 975.651 keV K-line together with additional conversion lines down to about 480 keV; if each line's position deviates from a single linear calibration by more than the quoted systematic uncertainty, or if the K-line residual to the simulation-corrected prediction does not reproduce the ~1.2 keV offset, the linearity and calibration-uncertainty claims fail.","supporting_citations":[],"review_version":1}