Pith. sign in

REVIEW 2 major objections 5 minor 6 cited by

A chiral X17 boson can explain the ATOMKI anomalies, but only in parameter space already excluded by atomic parity violation and KLOE-2.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

T0 review · deepseek-v4-flash

2026-08-03 00:11 UTC pith:F2KRVB7T

load-bearing objection A careful, transparent chiral-X17 fit that shows tension with APV and low-mass electron searches, but the central claim rests on the 12C(17.23) vector-matching input the paper flags but does not fully test. the 2 major comments →

arxiv 2602.11263 v1 pith:F2KRVB7T submitted 2026-02-11 hep-ph

The X17 with Chiral Couplings

Max H. Fieg , Toni M\"akel\"a , Tim M.P. Tait , Mi\v{s}a Toman This is my paper
classification hep-ph
keywords X17 bosonATOMKI anomalychiral couplingsaxial-vector currentatomic parity violationKLOE-2NA6412C(17.23)
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper tests whether a spin-1 X17 boson with genuinely chiral couplings to quarks — both vector and axial-vector, as in the Standard Model weak interactions — can explain the reported ATOMKI anomalies in 8Be, 12C, and 4He. It finds that a fit at 99% confidence is possible, but the best-fit region is in tension with null results from atomic parity-violation searches and from KLOE-2 and NA64, which bound new light particles coupled to electrons. The tension is traced to the 12C(17.23) transition: its relatively large reported excess drives the fit toward neutron couplings that run into the excluded zone. If the carbon measurement is removed from the fit, the remaining beryllium and helium anomalies leave an open region compatible with all considered constraints, and with the electron coupling suggested by the recent PADME excess.

Core claim

The central claim is that a chiral spin-1 X17 (with both vector and axial-vector couplings to quarks and nucleons) can survive the ATOMKI data as a 99% CL fit, but not without confronting exclusion limits: the region favored by the data is ruled out by a combination of atomic parity violation in cesium and the KLOE-2 bound on electron-coupled bosons, with NA64 close behind. The paper shows quantitatively that this tension is driven by the magnitude of the reported 12C(17.23) excess, which demands a large vector coupling to neutrons. When carbon is excluded, the remaining anomalies (8Be(18.15), 8Be(17.64), 4He) are consistent with all constraints in an open region of parameter space. The auth

What carries the argument

The analysis is built on a nuclear effective field theory in which the X couples to isospin-conserving and isospin-violating vector and axial-vector currents of nucleons. Vector couplings are anchored to measured M1 photon widths via ratios of matrix elements, so they inherit the photon data; axial-vector couplings require nuclear-theory matrix elements, especially the shell-model prediction for 12C(17.23), which the authors note over-predicts the M1 photon width by a factor of about 5.4. The paper tunes the electron vector coupling to cancel the SINDRUM-I pion-decay constraint, then scans the neutron coupling plane, fits the proton couplings and mass to the ATOMKI data, and overlays constra

Load-bearing premise

The load-bearing input is the shell-model prediction for the axial-vector matrix element of the 12C(17.23) transition — which the paper itself notes over-predicts the measured photon width by a factor of about 5.4 — because it is what pushes the best-fit region into the excluded zone; if this matrix element (or the state's 1− assignment) is wrong, the claimed tension with atomic parity violation and KLOE-2 may disappear.

What would settle it

Measure the M1 photon width of 12C(17.23) with improved precision and compare to the shell-model prediction, and/or determine the spin-parity of the state unambiguously; alternatively, improve the shell-model calculation so it reproduces the 44 eV width. If a revised axial-vector matrix element is much smaller than the current one, the best-fit region moves away from the excluded couplings and the tension reported in this paper would not persist.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • A chiral X17 interpretation of ATOMKI that explains 12C(17.23) must already be in significant tension with atomic parity-violation and electron-beam-dump searches, so the scenario is not parameter-free — it needs a specific tuned electron coupling to survive even the pion-decay constraint.
  • Without the 12C(17.23) excess, the remaining ATOMKI anomalies (the two beryllium transitions and helium) are compatible with all currently considered constraints at 99% CL, leaving a viable region for a chiral X17.
  • The electron coupling implied by the fit, |e ϵVe| ~ 1e-2, is of the same order as the value required to explain the recent PADME excess, making PADME a direct experimental check of the scenario.
  • The paper's explicit factor-of-five variation of the carbon axial-vector width does not remove the tension, indicating the conclusion is robust to that normalization but sensitive to the assumed quantum numbers of the 12C(17.23) state.

Where Pith is reading between the lines

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

  • If future data establish that the 12C(17.23) resonance is not a 1− state, the paper's central tension dissolves rather than being merely softened: a pseudoscalar X17 would again be viable, a possibility the authors explicitly leave open.
  • The paper's assumption that the 4He measurement carries the same relative uncertainty as the 8Be(18.15) measurement is a guess; a dedicated experimental uncertainty for the helium excess could shrink or expand the allowed region enough to change the outcome.
  • The tuned electron coupling, singled out to evade pion-decay limits, creates a sharp prediction: if X17 is real and chiral, PADME should observe a resonance at a coupling around |eϵVe| ≈ few × 1e-4; a null result at that strength would directly falsify this class of models.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 5 minor

Summary. The paper studies the hypothesis that the ATOMKI anomalies are due to a new spin-1 boson, X17, with chiral (simultaneous vector and axial-vector) couplings to nucleons, rather than purely vector or purely axial couplings considered in previous work. Using the nuclear EFT formalism of Feng, Tait, and Verhaaren, the authors compute the exotic decay widths for 8Be(18.15), 8Be(17.64), 12C(17.23), and 4He, fit the quark-level couplings to the reported ATOMKI branching ratios, and compare the resulting 99% CL regions with external constraints from atomic parity violation, KLOE-2, NA64, SINDRUM-I, and NA48. They find a region that accommodates all ATOMKI measurements at 99% CL, but that region is tension with APV and direct electron-coupling bounds, a tension driven primarily by the 12C(17.23) measurement. They show that removing the 12C measurement opens an unexcluded region for the remaining beryllium and helium observations.

Significance. If the ATOMKI data and the standard nuclear assignments are taken at face value, this is a useful and nontrivial negative result: a spin-1 X17 with chiral couplings cannot simultaneously explain the reported ATOMKI anomalies and evade APV/KLOE-2/NA64 constraints. The paper is transparent about the main caveat, the poorly-determined axial-vector matrix element for 12C, and it explicitly explores the effect of removing the 12C measurement. The EFT derivation is standard, the matching of vector couplings to measured photon widths is a strong feature, and the inclusion of PADME and the recent mass-profile fit adds context. The main weakness is that the robustness tests do not actually probe the load-bearing part of the 12C constraint, as discussed below.

major comments (2)
  1. [Secs. II and IV, App. B.3, Eqs. (B18)-(B19)] The robustness test for the 12C constraint varies only the axial-vector width ΓC_X,A by factors of 5. At the fitted couplings |εA_p − εA_n| ≲ 3×10^-3, Eq. (B19) gives ΓC_X,A/Γγ ≈ 2×10^-7, a few percent of the measured B_X = 3.6×10^-6. Even a factor-5 change leaves the total 12C width essentially unaffected. The carbon band in Fig. 1 is therefore set by the vector-matched width Eq. (B18), which assumes the reported excess is real, the state is a 1^- isovector resonance, and the E1 matching is exact. The statement that 'even this expanded uncertainty does not significantly change our conclusions' thus tests the wrong quantity. If the 12C assignment or excess fails, Fig. 2 shows the remaining Be/He fit has an unexcluded region. Please vary the vector normalization in Eq. (B18) by a factor of 2-5, or explicitly state that only the axial uncertainty has been varied and that the central tensio
  2. [Eq. (B7)] The expression for the beryllium vector width ΓBe_X,V reads [w0(εV_p + εV_n) + w1(εA_p − εA_n)]^2. The second term should almost certainly be w1(εV_p − εV_n), consistent with Eq. (B9) and the vector-current decomposition in Eqs. (B1)-(B2). If this expression was used in the scan, the 8Be(17.64) fit would incorrectly mix axial couplings into the vector width, potentially affecting the fit. Please correct the typo and confirm that the numerical results are unchanged.
minor comments (5)
  1. [Sec. II] Typo: 'does does not significantly change' should read 'does not significantly change'.
  2. [Sec. IV] The phrase 'They rule out 3 the best-fit region' is garbled by the footnote marker; the footnote should be placed after 'rule out' or the sentence restructured.
  3. [Fig. 2 caption] The last sentence repeats the blue-region description already given; please remove the duplication.
  4. [App. B.3] The phrase 'dimension (5) 3' is unclear; it should read 'dimension 5' or 'dimension-5 operator'.
  5. [Sec. III, Eq. (5)] The APV constraint is given without an explicit confidence level; please state the CL from Ref. [30].

Circularity Check

0 steps flagged

No circularity: the ATOMKI data are fitted, and the load-bearing tension claim is a comparison against independent external constraints (APV, KLOE-2, NA64, SINDRUM-I).

full rationale

The derivation chain is not circular. The paper explicitly fits the quark/electron couplings to the ATOMKI B_X measurements (Sec. IV: 'we fit the proton couplings ... to best fit the measurements in table I'), so the abstract's statement that it is 'possible to accommodate the reported ATOMKI signals' is an honest report of a fit, not a prediction of the fitted data. The load-bearing tension claim is a projection of externally measured constraints — SINDRUM-I (Eq. 3), KLOE-2/NA64 on electron couplings, and Cesium atomic parity violation (Eq. 5) — onto that best-fit region; these are independent of the fitted ATOMKI values. The nuclear matrix elements are taken from external groups (Refs. [13,17,23,31]), and the m_X likelihood is from Ref. [9], not from the present authors. The self-citation to Ref. [15] provides the nuclear-EFT matching formulas (e.g., Eq. B18), but this is a published formalism reproduced explicitly in the paper, not an unverified uniqueness claim, and the formulas are not defined in terms of the fitted ATOMKI parameters. The paper's own caveat (App. B.3) that the shell-model 12C photon width is 251 eV vs the measured 44 eV is a limitation/uncertainty in an external input, not a circular reduction; the central conclusion's sensitivity to the 12C input is tested by the removal counterfactual in Fig. 2 and acknowledged in Sec. V. Thus no step reduces to its own input by construction.

Axiom & Free-Parameter Ledger

6 free parameters · 6 axioms · 0 invented entities

The paper's contribution is a fit, not a first-principles derivation: six couplings/parameters are scanned or fitted to the same ATOMKI data whose 'accommodation' is claimed, and the central tension result depends on external nuclear matrix elements whose dominant uncertainty is handled with ad hoc inflation benchmarks (50/100%) rather than a computed systematic error. The heaviest upstream inputs are the carbon axial matrix element of Ref [17] (whose companion photon-width prediction is off by ~5.4×) and the assumed helium error bar. No new particles or mediators are introduced: the X boson is inherited from the ATOMKI hypothesis.

free parameters (6)
  • neutron vector coupling ϵV_n = scanned ±0.008; best-fit |ϵV_n|≈0.004
    Scanned plane; the ATOMKI fit favors |ϵV_n|≈0.004, driven by the 12C measurement.
  • neutron axial coupling ϵA_n = scanned ±0.003; best-fit ≈0
    Scanned plane; best-fit region prefers small axial neutron coupling.
  • proton couplings ϵV_p, ϵA_p = fit per scan point; |ϵV_p|<8e-4
    Fitted to the four ATOMKI measurements subject to the protophobic NA48 bound.
  • X mass mX = ≈16.9 MeV
    Fitted against the combined ATOMKI/MEG-II/VNU/PADME likelihood profile of Ref [9]; effectively pinned.
  • electron vector coupling eϵV_e = |eϵV_e|≈O(10^-2)
    Tuned via Eq. (4) to cancel the SINDRUM-I bound — a constraint-satisfaction condition, not a fit.
  • axial matrix-element uncertainty inflation = ±50% and ±100% benchmarks
    Ad hoc theory-uncertainty factors on the C and He axial widths; required for a 99% CL ATOMKI-consistent region to exist.
axioms (6)
  • domain assumption The nucleus-level EFT of Ref [15] correctly maps nucleon-level (axial-)vector couplings to the 8Be, 12C, 4He decay amplitudes.
    The formalism is inherited from a paper with overlapping authorship (Tait); the present paper adds no first-principles derivation of the EFT itself.
  • domain assumption The axial-vector nuclear matrix elements for C and He (Refs [17,23]) are correct within the assigned benchmark uncertainties.
    The carbon shell-model input over-predicts the measured M1 photon width of 12C(17.23) by ≈5.4× (251 eV vs 44 eV), App. B.3; the benchmark 50–100% errors are 'arbitrary' (paper's word).
  • domain assumption 12C(17.23) is well described as a 1− resonance.
    Authors note (Sec. V, footnote 4) that the shell-model failure may indicate the state is not a 1− resonance; if so the axial analysis and even the pseudoscalar exclusion would need revisiting.
  • domain assumption The 4He measurement σX/σE0=0.2 (no quoted uncertainty) has the same relative error as 8Be(18.15).
    Assumed in §III/Table I; the fit's helium constraint inherits this.
  • domain assumption X decays to e+e- with 100% branching fraction.
    Table I footnote; all BX values are normalized this way, so decays to other final states would rescale every fit.
  • standard math Standard QFT decay-width formulas and SM inputs (α, nucleon spin fractions Δu, Δd, measured Γγ values) are correct.
    Appendix B uses these without derivation; they are uncontroversial inputs.

pith-pipeline@v1.3.0-alltime-deepseek · 14919 in / 18288 out tokens · 170220 ms · 2026-08-03T00:11:08.533790+00:00 · methodology

0 comments
read the original abstract

In recent years, the ATOMKI collaboration has performed a series of measurements of excited nuclei, observing a resonant excess of electron-positron pairs at large opening angles compared to the Standard Model prediction. The excess has been hypothesized to be due to the production of a new spin-1 or spin-0 particle, X17, with a mass of about 17 MeV. Recently, the PADME experiment has reported an excess in the $e^+e^-$ cross section at center-of-mass energies near 17 MeV, perhaps further hinting at the existence of a new state. Studies of the spin-1 case have hitherto focused on either vector {\em or} axial-vector couplings to quarks and leptons, whereas UV theories more naturally produce {\em both} vector and axial-vector (\textit{i.e.} chiral) couplings, analogous to the Standard Model weak interactions. We consider the ATOMKI anomalies in the context of an $X$ with chiral couplings to quarks and explore the parameter space that can explain the ATOMKI anomalies, contrasting them with experimental constraints. We find that it is possible to accommodate the reported ATOMKI signals. However, the $99\%$ CL region is in tension with null results from searches for atomic parity violation and direct searches for new low mass physics coupled to electrons. This tension is found to be driven by the magnitude of the reported excess in the transition of $^{12}{\rm C}(17.23)$, which drives the best-fit region towards excluded couplings.

Figures

Figures reproduced from arXiv: 2602.11263 by Max H. Fieg, Mi\v{s}a Toman, Tim M.P. Tait, Toni M\"akel\"a.

Figure 1
Figure 1. Figure 1: FIG. 1. The result of the fit to the ATOMKI measurements in table [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. The result of the fit to the ATOMKI measurements in table [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Forward citations

Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. The X17 Existence Hinted at by Nuclear Reactor Neutrinos

    hep-ph 2026-05 unverdicted novelty 6.0

    Reactor neutrino CEvNS data corroborates the X17 particle by constraining its neutrino and nuclear couplings to a unique region when combined with other neutrino measurements.

  2. Flavor specific chiral $U(1)_X$ framework for explaining the ATOMKI anomaly

    hep-ph 2026-04 conditional novelty 6.0

    A gauged, flavor-specific U(1)_X two-Higgs-doublet model can realize the axial-vector Z' couplings needed to explain the ATOMKI 8Be and 4He anomalies while evading current bounds.

  3. Flavor specific chiral $U(1)_X$ framework for explaining the ATOMKI anomaly

    hep-ph 2026-04 unverdicted novelty 5.0

    A chiral flavor-specific U(1)_X model with two Higgs doublets accommodates the ATOMKI 17 MeV anomaly via a Z' boson whose parameter space remains consistent with atomic parity violation, beam dump, meson decay, and ne...

  4. The X17 Existence Hinted at by Nuclear Reactor Neutrinos

    hep-ph 2026-05 unverdicted novelty 4.0

    Reactor neutrino data from CONUS+ and Dresden-II combined with COHERENT and IceCube data singles out a region of neutrino and nuclear couplings consistent with the X17 particle.

  5. Where to find $X(17)$?

    hep-ph 2026-01 reject novelty 4.0

    Combining existing bounds with a new parity-violating Møller asymmetry constraint, the paper's body claims no surviving parameter space for scalar, pseudoscalar, vector, axial-vector, or V±A X(17)-electron couplings.

  6. Constraints on a Light Leptophilic Scalar from Dark-Sector Couplings

    hep-ph 2026-05 unverdicted novelty 3.0

    A parameter space analysis of a leptophilic scalar mediator model for Majorana dark matter yields a viable sub-GeV region after applying relic density, cosmological, astrophysical, and laboratory constraints.

Reference graph

Works this paper leans on

35 extracted references · 20 linked inside Pith · cited by 4 Pith papers

  1. [1]

    Beryllium There are two relevant 1 + excited states with compa- rable energy levels: a mostly isoscalar state 8Be(18.15) and a mostly isovector state 8Be(17.64) (there is isospin mixing and breaking of the nearby states, as we will dis- cuss in more detail). The anomaly was first measured and reported for the isoscalar state [1], with the best fit for the...

  2. [2]

    A parity even 4He(20.21) state withJ P = 0 + and a parity odd 4He(21.01) withJ P = 0 −

    Helium 4He has two relevant excited states. A parity even 4He(20.21) state withJ P = 0 + and a parity odd 4He(21.01) withJ P = 0 −. AnXwith mixed vector and axial-vector couplings to quarks could be produced in the decay of either excited state. The ATOMKI col- laboration ran the experiment at an intermediate energy, so that both states would comparably c...

  3. [3]

    Carbon The ATOMKI collaboration also observed an ex- cess in the decay of the 1 − excited state of carbon, 12C(17.23) [5]. The best fit width of the excited state decaying toX, multiplied by theX→e +e− branching fraction and normalized to the partial decay to photons, was reported to be Γ(12C(17.23)→ 12C +X) Γ(12C(17.23)→ 12C +γ) BF(X→e +e−) = (3.6±0.3)×1...

  4. [4]

    The am- plitude for the decay of the excited state then reads M=M V +MA =C Be V Λ−1ϵµναβ p∗ µϵ∗ νpαϵX β +C Be A Λϵ∗ µϵX µ

    Beryllium The leading nucleus EFT operator contributing to the exotic decay of the mostly iso-vector state, Be(17.64), is O5 =C Be V Λ−1N † 0 ϵµναβ ∂µN ∗ ν ∂αXβ,O 3 =C Be A ΛN † 0 N ∗ µX µ, (B5) where the first term is the vector piece, the second is the axial-vector,N 0 (N ∗) is the ground (excited) state and Λ is a scale with dimensions of energy. The a...

  5. [5]

    32πm2 N∗ ×p X 1 + p2 X 3m2 X (B6) and ΓBe X,V = w0(εV p +ε V n ) +w 1(εA p −ε A n ) 2 × α C2 V,Be (w2 0 +w 2

  6. [6]

    Due to the isospin mixing and breaking of the phys- ical excited nuclear state of beryllium, care must be taken when matching the nucleus EFT to the nucleon EFT

    12Λ2 p3 X , (B7) wherew 0, w1 are coefficients that describe the excited nuclear state which we now discuss. Due to the isospin mixing and breaking of the phys- ical excited nuclear state of beryllium, care must be taken when matching the nucleus EFT to the nucleon EFT. The nucleon level EFT describing the transition is thus composed of a linear combinati...

  7. [7]

    The experiment was run at an intermediate energy, such that both excited states would be produced

    Helium As discussed above, there are two relevant excited states for helium, 4He(21.01) and 4He(20.21), which have J P quantum numbers of 0 − and 0 +, respectively. The experiment was run at an intermediate energy, such that both excited states would be produced. The relevant quantity is then the totalXproduction cross sectionσ X , related to the branchin...

  8. [8]

    The leading operator for anXwith (axial-)vector transition is of dimension (5) 3

    Carbon The excited state of carbon, 12C(17.23), decays via an isovector transition. The leading operator for anXwith (axial-)vector transition is of dimension (5) 3. The effec- tive operator at the nucleus level for the isospin changing decay is then CA,C ϵA p −ϵ A n 2 ! ΛN † 0 N µ ∗ Xµ + CV,C Λ eϵV p −eϵ V n 2 ! N † 0 ϵµναβ (∂µN∗ν )(∂αXβ), (B16) where th...

  9. [9]

    Observation of Anomalous Internal Pair Creation in Be8 : A Possible Indication of a Light, Neutral Boson,

    A. J. Krasznahorkayet al., “Observation of Anomalous Internal Pair Creation in Be8 : A Possible Indication of a Light, Neutral Boson,”Phys. Rev. Lett.116no. 4, (2016) 042501,arXiv:1504.01527 [nucl-ex]

    Pith/arXiv arXiv 2016

  10. [10]

    New results on the Be-8 anomaly,

    A. J. Krasznahorkayet al., “New results on the Be-8 anomaly,”PoSBORMIO2017(2017) 036

    2017

  11. [11]

    New results on the 8Be anomaly,

    A. J. Krasznahorkayet al., “New results on the 8Be anomaly,”J. Phys. Conf. Ser.1056no. 1, (2018) 012028

    2018

  12. [12]

    On the creation of the 17 MeV X boson in the 17.6 MeV M1 transition of 8Be,

    A. J. Krasznahorkay, M. Csatl´ os, L. Csige, J. Guly´ as, T. J. Ketel, A. Krasznahorkay, I. Kuti, ´A. Nagy, B. M. Nyak´ o, N. Sas, and J. Tim´ ar, “On the creation of the 17 MeV X boson in the 17.6 MeV M1 transition of 8Be,” EPJ Web Conf.142(2017) 01019. https://cds.cern.ch/record/2275461

    arXiv 2017

  13. [13]

    New anomaly observed in C12 supports the existence and the vector character of the hypothetical X17 boson,

    A. J. Krasznahorkayet al., “New anomaly observed in C12 supports the existence and the vector character of the hypothetical X17 boson,”Phys. Rev. C106no. 6, (2022) L061601,arXiv:2209.10795 [nucl-ex]

    Pith/arXiv arXiv 2022

  14. [14]

    New evidence supporting the existence of the hypothetic X17 particle,

    A. J. Krasznahorkayet al., “New evidence supporting the existence of the hypothetic X17 particle,” arXiv:1910.10459 [nucl-ex]

    Pith/arXiv arXiv 1910

  15. [15]

    Checking the 8Be Anomaly with a Two-Arm Electron Positron Pair Spectrometer,

    T. T. Anhet al., “Checking the 8Be Anomaly with a Two-Arm Electron Positron Pair Spectrometer,” Universe10no. 4, (2024) 168,arXiv:2401.11676 [nucl-ex]. [8]MEG IICollaboration, K. Afanacievet al., “Search for the X17 particle in 7Li(p,e +e−)8Be processes with the MEG II detector,”Eur. Phys. J. C85no. 7, (2025) 763,arXiv:2411.07994 [nucl-ex]

    Pith/arXiv arXiv 2024

  16. [16]

    Combined Evidence for theX 17 Boson After PADME Results on Resonant Production in Positron Annihilation,

    F. Arias-Arag´ on, G. G. di Cortona, E. Nardi, and C. Toni, “Combined Evidence for theX 17 Boson After PADME Results on Resonant Production in Positron Annihilation,”arXiv:2504.11439 [hep-ph]

    Pith/arXiv arXiv

  17. [17]

    Hunting the elusiveX17 in CEνNS at the ESS,

    J. Cederk¨ all, Y. Hi¸ cyılmaz, E. Lytken, S. Moretti, and J. Rathsman, “Hunting the elusiveX17 in CEνNS at the ESS,”arXiv:2509.15128 [hep-ph]

    arXiv

  18. [18]

    Search for a new 17 MeV resonance via e+e− annihilation with the PADME Experiment,

    F. Bossiet al., “Search for a new 17 MeV resonance via e+e− annihilation with the PADME Experiment,” arXiv:2505.24797 [hep-ex]

    arXiv

  19. [19]

    Protophobic Fifth-Force Interpretation of the Observed Anomaly in 8Be Nuclear Transitions,

    J. L. Feng, B. Fornal, I. Galon, S. Gardner, J. Smolinsky, T. M. P. Tait, and P. Tanedo, “Protophobic Fifth-Force Interpretation of the Observed Anomaly in 8Be Nuclear Transitions,”Phys. Rev. Lett. 117no. 7, (2016) 071803,arXiv:1604.07411 [hep-ph]

    Pith/arXiv arXiv 2016

  20. [20]

    Light axial vector bosons, nuclear transitions, and the 8Be anomaly,

    J. Kozaczuk, D. E. Morrissey, and S. R. Stroberg, “Light axial vector bosons, nuclear transitions, and the 8Be anomaly,”Phys. Rev. D95no. 11, (2017) 115024, arXiv:1612.01525 [hep-ph]

    Pith/arXiv arXiv 2017

  21. [21]

    Particle physics models for the 17 MeV anomaly in beryllium nuclear decays,

    J. L. Feng, B. Fornal, I. Galon, S. Gardner, J. Smolinsky, T. M. P. Tait, and P. Tanedo, “Particle physics models for the 17 MeV anomaly in beryllium nuclear decays,”Phys. Rev. D95no. 3, (2017) 035017, arXiv:1608.03591 [hep-ph]

    Pith/arXiv arXiv 2017

  22. [22]

    Dynamical Evidence For a Fifth Force Explanation of the ATOMKI Nuclear Anomalies,

    J. L. Feng, T. M. P. Tait, and C. B. Verhaaren, “Dynamical Evidence For a Fifth Force Explanation of the ATOMKI Nuclear Anomalies,”Phys. Rev. D102 no. 3, (2020) 036016,arXiv:2006.01151 [hep-ph]

    Pith/arXiv arXiv 2020

  23. [23]

    An updated view on the ATOMKI nuclear anomalies,

    D. Barducci and C. Toni, “An updated view on the ATOMKI nuclear anomalies,”JHEP02(2023) 154, arXiv:2212.06453 [hep-ph]. [Erratum: JHEP 07, 168 (2023)]

    Pith/arXiv arXiv 2023

  24. [24]

    Constraining the axial-vector X17 interpretation with 12C data,

    C. J. G. Mommers and M. Vanderhaeghen, “Constraining the axial-vector X17 interpretation with 12C data,”Phys. Lett. B858(2024) 139031, arXiv:2406.08143 [hep-ph]

    Pith/arXiv arXiv 2024

  25. [25]

    Light Weakly Coupled Axial Forces: Models, Constraints, and Projections,

    Y. Kahn, G. Krnjaic, S. Mishra-Sharma, and T. M. P. Tait, “Light Weakly Coupled Axial Forces: Models, Constraints, and Projections,”JHEP05(2017) 002, arXiv:1609.09072 [hep-ph]

    Pith/arXiv arXiv 2017

  26. [26]

    Pion decay constraints on exotic 17 MeV vector bosons,

    M. Hostert and M. Pospelov, “Pion decay constraints on exotic 17 MeV vector bosons,”Phys. Rev. D108 no. 5, (2023) 055011,arXiv:2306.15077 [hep-ph]

    Pith/arXiv arXiv 2023

  27. [27]

    Limit on the production of a low-mass vector boson in e +e− →Uγ, U→e +e− with the KLOE experiment,

    A. Anastasiet al., “Limit on the production of a low-mass vector boson in e +e− →Uγ, U→e +e− with the KLOE experiment,”Phys. Lett. B750(2015) 633–637,arXiv:1509.00740 [hep-ex]. [21]NA64Collaboration, D. Banerjeeet al., “Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN,”Phys. Rev. Lett. 120no. 23, (2018) 231802...

    Pith/arXiv arXiv 2015

  28. [28]

    Four-body calculation for excited states of He-4,

    W. Horiuchi and Y. Suzuki, “Four-body calculation for excited states of He-4,”Int. J. Mod. Phys. A24(2009) 2134–2141

    2009

  29. [29]

    An Update of the Hypothetical X17 Particle,

    A. J. Krasznahorky, A. Krasznahorkay, M. Csatl´ os, J. Tim´ ar, M. Begala, A. Krak´ o, I. Rajta, I. Vajda, and N. J. Sas, “An Update of the Hypothetical X17 Particle,”Universe10no. 11, (2024) 409, arXiv:2409.16300 [nucl-ex]

    Pith/arXiv arXiv 2024

  30. [30]

    Observation of the X17 anomaly in the decay of the Giant Dipole Resonance of 8Be,

    A. J. Krasznahorkay, A. Krasznahorkay, M. Csatl´ os, L. Csige, J. Tim´ ar, M. Begala, A. Krak´ o, I. Rajta, and I. Vajda, “Observation of the X17 anomaly in the decay of the Giant Dipole Resonance of 8Be,” arXiv:2308.06473 [nucl-ex]. [26]MEG IICollaboration, A. M. Baldiniet al., “The design of the MEG II experiment,”Eur. Phys. J. C78 no. 5, (2018) 380,arX...

    Pith/arXiv arXiv 2018

  31. [31]

    The SINDRUM-I Experiment,

    R. Eichler and C. Grab, “The SINDRUM-I Experiment,”SciPost Phys. Proc.5(2021) 007. [28]NA48/2Collaboration, J. R. Batleyet al., “Search for the dark photon inπ 0 decays,”Phys. Lett. B746 (2015) 178–185,arXiv:1504.00607 [hep-ex]

    Pith/arXiv arXiv 2021

  32. [32]

    Precision determination of electroweak coupling from atomic parity violation and implications for particle physics,

    S. G. Porsev, K. Beloy, and A. Derevianko, “Precision determination of electroweak coupling from atomic parity violation and implications for particle physics,” Phys. Rev. Lett.102(2009) 181601,arXiv:0902.0335 [hep-ph]

    Pith/arXiv arXiv 2009

  33. [33]

    Probing low-mass vector bosons with parity nonconservation and nuclear anapole moment measurements in atoms and molecules,

    V. A. Dzuba, V. V. Flambaum, and Y. V. Stadnik, “Probing low-mass vector bosons with parity nonconservation and nuclear anapole moment measurements in atoms and molecules,”Phys. Rev. Lett.119no. 22, (2017) 223201,arXiv:1709.10009 [physics.atom-ph]

    Pith/arXiv arXiv 2017

  34. [34]

    Quantum Monte Carlo calculations of electromagnetic transitions in 8Be with meson-exchange 11 currents derived from chiral effective field theory,

    S. Pastore, R. B. Wiringa, S. C. Pieper, and R. Schiavilla, “Quantum Monte Carlo calculations of electromagnetic transitions in 8Be with meson-exchange 11 currents derived from chiral effective field theory,” Phys. Rev. C90no. 2, (2014) 024321,arXiv:1406.2343 [nucl-th]

    Pith/arXiv arXiv 2014

  35. [35]

    http://www.nndc.bnl.gov/ensdf

    National Nuclear Data Center. http://www.nndc.bnl.gov/ensdf