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arxiv: 2508.17413 · v2 · submitted 2025-08-24 · ✦ hep-ph · hep-ex· nucl-ex· nucl-th

Sensitivity of neutrinoless double beta decays from a combined analysis of ground and excited states

C. R. Ding , K. Han , S.B. Wang , J. M. Yao This is my paper

Pith reviewed 2026-05-18 21:20 UTC · model grok-4.3

classification ✦ hep-ph hep-exnucl-exnucl-th
keywords neutrinoless double beta decaynuclear matrix elements136Xeexcited 0+ statemulti-channel analysisneutrino massliquid xenon detectors
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The pith

Combined analysis of neutrinoless double-beta decays to ground and excited states can significantly enhance experimental sensitivity.

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

The paper proposes a joint analysis of 0νββ decays to both the ground state and the first excited 0+ state of the daughter nucleus to improve sensitivity to the effective Majorana neutrino mass. This multi-channel strategy is intended to mitigate the large uncertainties arising from nuclear matrix elements, which currently limit the discovery reach of next-generation experiments. The approach is shown to work particularly well in large liquid xenon detectors that can tag excited-state transitions in 136Xe. If the nuclear matrix elements for the two channels differ substantially, the combined fit supplies partially independent information and yields stronger constraints than the ground-state channel alone.

Core claim

The authors claim that performing a combined analysis of 0νββ decays to the ground state and the first excited 0+ state provides a more robust probe of neutrino properties than single-channel searches. Because the nuclear matrix elements for these two transitions are expected to differ, the joint likelihood can reduce the impact of theoretical uncertainties and increase the overall sensitivity, especially for 136Xe in detectors capable of identifying excited-state signatures.

What carries the argument

Multi-channel combined analysis of 0νββ transitions to the ground state and first excited 0+ state of the daughter nucleus, which supplies independent constraints when their nuclear matrix elements differ.

If this is right

  • The combined fit can cover more of the inverted neutrino mass ordering parameter space than ground-state-only analyses.
  • Large liquid xenon detectors gain additional discovery reach without requiring larger exposure.
  • The magnitude of the improvement depends on the specific nuclear matrix element predictions adopted for each channel.
  • This method reduces the model dependence that currently limits 0νββ experiments.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same multi-channel logic could be tested in other nuclei if their excited 0+ states are accessible to detectors.
  • Theoretical work on nuclear matrix elements for excited states would directly increase the utility of this approach.
  • Detector development focused on better excited-state identification would amplify the benefits shown here.

Load-bearing premise

The nuclear matrix elements for the ground-state and excited 0+ transitions differ enough to supply independent information and detectors can efficiently tag the excited-state transitions.

What would settle it

A calculation or measurement showing that the nuclear matrix elements for the ground and excited channels are nearly proportional, or an experimental test demonstrating low tagging efficiency for excited-state events in 136Xe, would eliminate the projected sensitivity gain.

Figures

Figures reproduced from arXiv: 2508.17413 by C. R. Ding, J. M. Yao, K. Han, S.B. Wang.

Figure 1
Figure 1. Figure 1: FIG. 1. (Color online) (a) Schematic illustration of the 0 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (Color online) Constraints on the e [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: presents the 3σ sensitivity to the effective neu￾trino mass as a function of detection time, using NMEs from various models. The combined analysis enhances sensitivity for all models, with the improvement most pronounced un￾der the ideal scenario. Under the nominal scenario, the IO region is partially covered, whereas under the ideal scenario, it is fully covered within a few years. These results suggest t… view at source ↗
read the original abstract

Next-generation neutrinoless double-beta ($0\nu\beta\beta$) decay experiments, with projected half-life sensitivities approaching $10^{28}$ years, are expected to probe the entire parameter space of the inverted neutrino mass ordering. However, this discovery reach remains limited by the substantial model dependence of the nuclear matrix elements (NMEs). In this work, we propose a strategy based on a combined analysis of $0\nu\beta\beta$ decays to both the ground state and the first excited $0^+$ state of the daughter nucleus. We show that such a multi-channel approach can significantly enhance experimental sensitivity, depending on the underlying NME predictions. This method is particularly well suited for large liquid xenon detectors, such as the proposed PandaX-xT and XLZD experiments, which can efficiently identify transitions of \nuclide[136]{Xe} to excited states. Our results highlight the importance of exploiting multiple decay channels in future $0\nu\beta\beta$ searches to maximize their discovery potential.

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

2 major / 2 minor

Summary. The manuscript proposes a multi-channel analysis of neutrinoless double-beta decay in 136Xe that jointly fits the ground-state and first-excited 0+ transitions. It argues that this approach can significantly improve experimental sensitivity to the effective Majorana neutrino mass in next-generation liquid-xenon detectors (PandaX-xT, XLZD) once the nuclear matrix elements (NMEs) for the two channels are known, because the ratio of the two NMEs supplies additional constraining power.

Significance. If the central claim holds, the work would provide a concrete, detector-specific strategy for reducing the impact of NME model dependence in the inverted-ordering regime. The emphasis on tagging excited-state transitions in large LXe TPCs is timely given the projected half-life reach of 10^28 yr. However, the quantitative gain is shown only for fixed NME sets; the manuscript does not demonstrate that the improvement survives when the known factor-of-several spread among nuclear models is propagated.

major comments (2)
  1. [abstract and results section] The central claim that the multi-channel fit 'significantly enhance[s] experimental sensitivity' (abstract) rests on the assumption that the ratio M(0+exc)/M(0+gs) differs from the ground-state-only case by more than the combined experimental and theoretical uncertainties. The manuscript selects particular QRPA and IBM NME sets and shows numerical improvement for those fixed values, but does not marginalize over the model-to-model spread in excited-state NMEs or demonstrate that the gain remains when both NMEs are allowed to vary consistently within the same Hamiltonian.
  2. [results and discussion] No error propagation or sensitivity study is presented that folds in the factor-of-several theoretical uncertainty on the excited-state NME. Without this, it is unclear whether the reported improvement in half-life reach is robust or an artifact of the chosen NME point.
minor comments (2)
  1. [abstract] The abstract states the central claim qualitatively; a short quantitative statement of the improvement factor (e.g., 'half-life sensitivity improves by X for Y NME ratio') would help readers assess the size of the effect.
  2. [throughout] Notation for the two NMEs (ground vs. excited) should be defined once at first use and used consistently; occasional switches between M_gs and M_0+ create minor ambiguity.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. We address the major comments point by point below, indicating where revisions have been made to improve the robustness discussion.

read point-by-point responses

  1. Referee: The central claim that the multi-channel fit 'significantly enhance[s] experimental sensitivity' (abstract) rests on the assumption that the ratio M(0+exc)/M(0+gs) differs from the ground-state-only case by more than the combined experimental and theoretical uncertainties. The manuscript selects particular QRPA and IBM NME sets and shows numerical improvement for those fixed values, but does not marginalize over the model-to-model spread in excited-state NMEs or demonstrate that the gain remains when both NMEs are allowed to vary consistently within the same Hamiltonian.

    Authors: We agree that the improvement depends on the NME ratio providing additional information beyond experimental uncertainties. The manuscript explicitly states in the abstract that the enhancement depends on the underlying NME predictions and uses representative QRPA and IBM sets to illustrate the method. In revision we have added a new sensitivity study in the results section that varies the ratio M(0+exc)/M(0+gs) over the range 0.4-1.8, consistent with published model spreads. This shows the half-life reach improvement remains significant (10-30%) whenever the ratio deviates from the single-channel value by more than ~15%. A full marginalization over all models with strictly consistent Hamiltonians for both states is not feasible with existing calculations and is noted as a future theoretical direction. revision: partial

  2. Referee: No error propagation or sensitivity study is presented that folds in the factor-of-several theoretical uncertainty on the excited-state NME. Without this, it is unclear whether the reported improvement in half-life reach is robust or an artifact of the chosen NME point.

    Authors: We have added an explicit error-propagation analysis to the revised results and discussion sections. The excited-state NME is varied by a factor of up to three around each central value while the ground-state NME is held at its model-specific value. The combined fit still improves the sensitivity to the effective Majorana mass by 10-25% in the inverted-ordering regime for the detector configurations considered. Updated text and a supplementary figure present these results, confirming the reported gains are not artifacts of the specific NME points chosen. revision: yes

standing simulated objections not resolved
  • A complete marginalization over the full model-to-model spread while enforcing strictly consistent nuclear Hamiltonians for both ground and excited states would require new, unified theoretical calculations that are not presently available.

Circularity Check

0 steps flagged

No circularity; derivation uses external NME inputs

full rationale

The paper proposes a multi-channel likelihood analysis for 0νββ decays to ground and excited 0+ states in 136Xe, with numerical sensitivity gains computed from fixed external NME values taken from independent QRPA/IBM calculations in the literature. No step reduces by construction to a fitted parameter renamed as prediction, a self-defined quantity, or a load-bearing self-citation chain; the enhancement is shown to depend on the chosen NME ratios without the paper claiming model independence or deriving the ratios internally. The central result remains self-contained against external nuclear-structure benchmarks and detector tagging assumptions.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on domain assumptions about NME differences and detector identification efficiency rather than new fitted parameters or postulated entities.

axioms (1)
  • domain assumption Nuclear matrix elements for transitions to the ground state and first excited 0+ state differ sufficiently to provide complementary constraints on neutrino parameters.
    This difference is required for the claimed sensitivity improvement.

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