REVIEW 2 major objections 3 minor 25 references
Remarks on strong phase shifts in weak nonleptonic baryon decays
T0 review · 2 major / 3 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read The paper proposes a single sign-parameterized formula, Eq. (10), that reproduces the strong phase shift $\delta_P-\delta_S$ under all three conventions used in the literature.
desk verdict Useful convention-compilation note whose central equation appears malformed as printed; fix the typo and it earns publication. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying object is the sign-parameterized arctangent formula, Eq. (10): $$\delta_P-\delta_S = 2\arctan\left(\frac{\$\beta$\,\mathrm{sign}}{\sqrt{\$alpha^{2}$+\$beta^{2}$}+\$\alpha$\,\mathrm{sign}}\right).$$ The sign constant encodes the convention-specific sign of the product of the S- and P-wave amplitudes, or the sign of $\sin(2\zeta)$, which is often not stated in experimental papers. The formula works because $\alpha$ is proportional to the cosine of the phase shift and $\beta$ to its sine, and the denominator $\sqrt{\alpha^2+\beta^2}+\alpha\,\mathrm{sign}$ selects the correct branch of the arctangent, returning an angle in $[-\pi,\pi]$ rather than only in the principal branch $[-\pi/2,\pi/2]$. One formula thus replaces the case-by-case branch corrections previously applied convention by convention.
What would settle it
Find a published baryon-decay analysis whose S- and P-wave amplitudes are defined with a phase convention that cannot be reduced to Eqs. (2), (6), or (7), or show that with a known sign the phase shift from Eq. (10) disagrees with the paper's reported value by anything other than an integer multiple of $\pi$; either result would disprove the claimed unification.
Extended reading notes
Core claim
The central claim is that the strong phase shift $\delta_P-\delta_S$ in any two-body nonleptonic baryon decay can be extracted from the measured $\alpha$ and $\beta$ by $$\delta_P-\delta_S = 2\arctan\left(\frac{\$\beta$\,\mathrm{sign}}{\sqrt{\$alpha^{2}$+\$beta^{2}$}+\$\alpha$\,\mathrm{sign}}\right),$$ where 'sign' is a constant equal to either $+1$ or $-1$. For the first convention, $\mathrm{sign}=+1$ reduces the formula to the expression recently proposed in Ref. [10]; for the second convention, sign is the sign of the product $e_S e_P$ of the real amplitudes; for the third, it is the sign of $\sin(2\zeta)$. The paper shows numerically, across the experiments collected in its table, that switching sign changes $\delta_P-\delta_S$ by $\pi$ but leaves $\tan(\delta_P-\delta_S)$ exactly unchanged, so the tangent is convention-independent while the angle itself carries a $\pi$ ambiguity. It further points out that in one published $\Xi^-\to\Lambda\pi^-$ analysis the reported $(\alpha,\delta_P-\delta_S)$ pair is internally inconsistent once this branch structure is respected.
Load-bearing premise
The unification assumes that every publication's convention is captured by one of the three parameterizations in Eqs. (2), (6), and (7), and that the relevant sign can in principle be identified; a fourth convention or a sign ambiguity that is not binary would break the formula.
Editorial extensions
If this is right
- The same measured pair $(\alpha,\beta)$ yields two possible phase shifts differing by $\pi$, and $\tan(\delta_P-\delta_S)$ is identical for both, so any global average that uses only the tangent is convention-independent.
- Published $\Lambda$, $\Xi$, and $\Lambda_c^+$ data can all be re-expressed in Eq. (10), with the sign usually recoverable from the original papers, as the table demonstrates.
- The E756 result on $\Xi^-\to\Lambda\pi^-$, which reported $\delta_P-\delta_S=0.06\pm0.09$ with $\alpha<0$ under the first convention, is internally inconsistent; applying Eq. (10) gives $-3.08\pm0.09$ rad for the same sign choice.
- BESIII's two solutions for $\Lambda_c^+\to\Xi^0K^+$, $-1.55\pm0.25$ rad and $1.59\pm0.25$ rad, correspond exactly to the two sign choices, so the measured large phase shift persists under the unified form.
- Future experimental papers on baryon weak decays should quote the sign or explicitly state the amplitude convention, so that phase-shift values can be combined without bookkeeping errors.
Reading between the lines
- If the same sign-parameterized formula is applied to future measurements in $\Lambda_b$ and $\Xi_b$ decays, the convention ambiguity should appear in the same two-branch form, because the standard S- and P-wave partial-wave decomposition has the same structure for any $1/2^+\to 1/2^+ + 0^-$ decay.
- The sign that resolves each measurement's branch can be compared with the sign of the product of S- and P-wave amplitudes predicted by a theoretical amplitude scheme, giving a consistency test that is independent of absolute phase conventions.
- A practical rule suggested by the paper, but not stated by it, is that data tables should report $\alpha$, $\beta$, and the sign rather than a phase-shift value alone, since the latter is not convention-free.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript reviews the conventions used in the literature for the strong phase shift δP−δS in two-body nonleptonic baryon decays, proposes Eq. (10) as a unified parameterization that accommodates three common amplitude parameterizations, and presents a table of phase shifts computed from published α, β, and ϕ values. The paper also discusses the impact of sign ambiguities on global averages and on CP-violation studies in baryon decays.
Significance. If the proposed formula and table are correct, the paper provides a compact and useful service to the baryon-CP community: it collects experimental results from different experiments, exposes the sign ambiguity, and offers a common language for comparing phase shifts. The underlying identity is standard, but the compilation and the explicit attention to the sign convention are useful. However, the central equation is not correctly displayed in the manuscript as provided, and the definition of the sign parameter is incomplete; both issues must be fixed before the paper can serve as a reliable reference.
major comments (2)
- [Eqs. (4) and (10)] The displayed form of Eq. (10), and likewise Eq. (4), is incomplete: it reads as 'δP−δS = 2 arctan β× signp α2 +β2 +α× sign', with no square root and no fraction bar. Taken literally, this expression is not the claimed phase-shift formula and cannot reproduce the values in Table 1. For example, in the E756 row (α=−0.458, β=−0.03, sign=+1) the literal expression gives about 0.24 rad, whereas the table lists −3.08±0.09 rad; the intended identity with √(α²+β²) in the denominator gives −3.08 rad. Because Eq. (10) is the central result, please correct the typesetting of Eqs. (4) and (10) and re-verify the table entries with the intended formula.
- [Definition of 'sign' in Eq. (10)] The constant 'sign' is introduced without an explicit mapping to the three conventions. For convention 2, α2 and β2 in Eq. (8) are proportional to eS eP, and for convention 3, α3 and β3 in Eq. (9) are proportional to sin(2ζ); in convention 1 the coefficient is positive. The paper should state that 'sign' equals the sign of the common coefficient, namely sign(2|S||P|/(|S|²+|P|²))=+1, sign(2eS eP/(|eS|²+|eP|²)), or sign(sin 2ζ), respectively. Without this identification, a reader cannot determine which value of sign to use for a given published analysis, and the table's 'unknown' entries are ambiguous between a convention-dependent and experimental source.
minor comments (3)
- [Eq. (4)] The text attributes Eq. (4) to Ref. [10] as 'the new formula', but the formula as shown is garbled; the same typographical correction needed for Eq. (10) applies here.
- [Table 1] The column heading 'Value of sign' should be clarified to indicate whether the sign is inferred from the amplitude convention or explicitly reported by the experiment; for rows with no entry the paper should state explicitly that the sign is unknown.
- [General] A one-line derivation of Eq. (10) using the identity tan(Δ/2)=sinΔ/(1+cosΔ) would help readers see why the formula is exact and why the sign choice changes δP−δS by π while leaving tan(δP−δS) invariant.
Circularity Check
No significant circularity: the unified phase-shift formula is a rearrangement of the standard α-β definitions, applied to external data.
full rationale
The paper makes no predictive claim that reduces to its own inputs. Equation (10) is an algebraic rearrangement of the defining relations α = 2|S||P| cos(δP−δS)/(|S|²+|P|²) and β = 2|S||P| sin(δP−δS)/(|S|²+|P|²), using tan(Δ/2) = sinΔ/(1+cosΔ); it is not fitted to data, and the 'sign' parameter is an explicitly declared convention choice rather than a fitted constant. The numerical table applies Eq. (10) to independently published α, β, and phase-shift values, and the agreement with previously reported phase shifts is a consistency check, not a derivation of those values. Citations to prior work (e.g., Refs. [10], [11], [13]) provide external experimental results or earlier formulas; none of the load-bearing steps is justified solely by a publication by the present authors. The paper also openly flags the practical limitation that the sign in some experimental conventions is unknown, which is an acknowledgement of ambiguity rather than a circular maneuver. No self-definitional step, fitted-input-as-prediction, or imported uniqueness theorem appears. A separate typographical presentation issue in Eq. (10) (missing radical or fraction bar in the extracted text) is a correctness concern, not a circularity concern.
Assumptions & free parameters
free parameters (1)
- sign =
+1 or -1 (chosen by convention, not fitted)
assumptions (3)
- domain assumption Lee-Yang partial-wave analysis: a spin-1/2 baryon decaying to spin-1/2 + 0− is fully described by S- and P-wave amplitudes.
- domain assumption The published experimental values of α, β, and ϕ in Table 1 are correct and mutually consistent.
- domain assumption CP conservation is assumed in the extraction of strong phases from data.
Cite this review
Pith. "Pith review of Remarks on strong phase shifts in weak nonleptonic baryon decays." pith.science (2026). https://pith.science/paper/VEF6WURY
@misc{pith2026241202170,
author = {Pith},
title = {Pith review of: Remarks on strong phase shifts in weak nonleptonic baryon decays},
year = {2026},
howpublished = {\url{https://pith.science/paper/VEF6WURY}},
note = {Machine review of arXiv:2412.02170}
}
abstract
A sizable strong-interaction phase shift in weak two-body nonleptonic baryon decay would enhance the possibility of discovering charge-conjugation parity ($CP$) violation in the baryon sector, which might help in the quest for understanding the matter-antimatter asymmetry in the universe. Over the past 60 years, empirical analyses involving different types of instruments, including fixed-target experiments and $e^+e^-$ colliders, have indicated that the phase shifts in nonleptonic hyperon decays are relatively small, below order ten degrees in size. A large phase shift, however, has been observed by BESIII in the decay of a charmed baryon into a hyperon and kaon, $\Lambda_c^+\to \Xi^0K^+$. In various experimental and theoretical studies on hyperon, charmed-baryon, and bottomed-baryon decays, different conventions have been adopted for defining the strong phases. It is important to be aware of this situation when obtaining global averages from different measurements and applying the results to future investigations on $CP$ violation among baryons. This paper gives an overview of the conventions employed in the literature for the strong phases and suggests a unified parameterization form applicable to the different alternatives. Numerical results under the unified parameterization form are also provided, which can serve as useful inputs to further pursuits of baryon $CP$ violation.
Figures
Reference graph
Works this paper leans on
-
[10]
Zhong HL, Xu FR, Cheng HY . Analysis of hadronic weak decays of charmed baryons in the topological diagrammatic approach, Phys Rev D 2024;109:114027
work page 2024
-
[1]
Sakharov AD, et al, Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe, Pisma Zh Eksp Teor Fiz 1967;5:32-35
work page 1967
-
[2]
Observation of direct CP vio- lation in KS,L→ππ decays, Phys Rev Lett 1999;83:22-27
KTeV Collaboration, Alavi-Harati A, et al. Observation of direct CP vio- lation in KS,L→ππ decays, Phys Rev Lett 1999;83:22-27
work page 1999
-
[3]
Observation of CP violation in charm decays, Phys Rev Lett 2019;122:211803
LHCb Collaboration, Aaij R, et al. Observation of CP violation in charm decays, Phys Rev Lett 2019;122:211803
work page 2019
-
[4]
Observation of several sources of CP violation in B+→π+π+π− decays, Phys Rev Lett 2020;124:031801
LHCb Collaboration, Aaij R, et al. Observation of several sources of CP violation in B+→π+π+π− decays, Phys Rev Lett 2020;124:031801
work page 2020
-
[5]
Measurement of matter-antimatter dif- ferences in beauty baryon decays, Nature Phys 2017;13:391-396
LHCb Collaboration, Aaij R, et al. Measurement of matter-antimatter dif- ferences in beauty baryon decays, Nature Phys 2017;13:391-396
work page 2017
-
[6]
LHCb Collaboration, Aaij R, et al. Study of Λ0 b and Ξ0 b decays to Λh+h′− and evidence for CP violation in Λ0 b→ ΛK+K− decays, arXiv: 2411.15441, 2024
-
[7]
Production and decay of polarized hyperon-antihyperon pairs, Chin Phys C 2023;47:052002
Sch ¨onning K, Batozskaya V , Adlarson P, et al. Production and decay of polarized hyperon-antihyperon pairs, Chin Phys C 2023;47:052002
work page 2023
Show all 25 references
-
[8]
General partial wave analysis of the decay of a hyperon of spin 1/2, Phys Rev 1957;108:1645-1647
Lee TD, Yang CN. General partial wave analysis of the decay of a hyperon of spin 1/2, Phys Rev 1957;108:1645-1647
1957
-
[9]
Review of particle physics, Phys Rev D 2024;110:030001
Particle Data Group, Navas S, et al. Review of particle physics, Phys Rev D 2024;110:030001
2024
-
[11]
Hyperon decays and CP nonconserva- tion, Phys Rev D 1986;34:833
Donoghue JF, He XG, Pakvasa S. Hyperon decays and CP nonconserva- tion, Phys Rev D 1986;34:833
1986
-
[12]
Complete determination of S U(3)F amplitudes and strong phase in Λ+ c → Ξ0K+, Phys Rev D 2024;109:L071302
Geng CQ, He XG, Jin XN, Liu CW, et al. Complete determination of S U(3)F amplitudes and strong phase in Λ+ c → Ξ0K+, Phys Rev D 2024;109:L071302
2024
-
[13]
First measurement of the decay asymmetry in the pure W-boson-exchange decay Λ+ c → Ξ0K+, Phys Rev Lett 2024;132:031801
BESIII Collaboration, Ablikim M, et al. First measurement of the decay asymmetry in the pure W-boson-exchange decay Λ+ c → Ξ0K+, Phys Rev Lett 2024;132:031801
2024
-
[14]
Measurement of the decay parameters of theΛ0 particle, Phys Rev 1963;129:1795-1807
Cronin JW, Overseth OE. Measurement of the decay parameters of theΛ0 particle, Phys Rev 1963;129:1795-1807
1963
-
[15]
Time reversal invariance in Λ0 decay, Phys Rev Lett 1967;19:391-393
Overseth OE, Roth RF. Time reversal invariance in Λ0 decay, Phys Rev Lett 1967;19:391-393
1967
-
[16]
Study of CP violation in hy- peron decays at super-charm-tau factories with a polarized electron beam, Phys Rev D 2022;105:116022
Salone N, Adlarson P, Batozskaya V , et al. Study of CP violation in hy- peron decays at super-charm-tau factories with a polarized electron beam, Phys Rev D 2022;105:116022
2022
-
[17]
Measurement of decay parameters for Ξ−→ Λπ− decay, Phys Rev Lett 2003;91:031601
FNAL E756 Collaboration, Chakravorty A, et al. Measurement of decay parameters for Ξ−→ Λπ− decay, Phys Rev Lett 2003;91:031601
2003
-
[18]
Pion-proton scattering below 150 Mev
Barnes SW, Winick H, Miyake K, et al. Pion-proton scattering below 150 Mev. II, Phys Rev 1960;117:238-242
1960
-
[19]
New measurement ofΞ−→ Λπ− decay parameters, Phys Rev Lett 2004;93:011802
HyperCP Collaboration, Huang M, et al. New measurement ofΞ−→ Λπ− decay parameters, Phys Rev Lett 2004;93:011802
2004
-
[20]
Probing C Psymmetry and weak phases with entangled double-strange baryons, Nature 2022;606:64-69
BESIII Collaboration, Ablikim M, et al. Probing C Psymmetry and weak phases with entangled double-strange baryons, Nature 2022;606:64-69
2022
-
[21]
Observation of Ξ− hyperon trans- verse polarization inψ(3686)→ Ξ− ¯Ξ+, Phys Rev D 2022;106:L091101
BESIII Collaboration, Ablikim M, et al. Observation of Ξ− hyperon trans- verse polarization inψ(3686)→ Ξ− ¯Ξ+, Phys Rev D 2022;106:L091101
2022
-
[22]
Investigation of the∆I = 1/2 rule and test of CP symmetry through the measurement of decay asymmetry parameters in Ξ− decays, Phys Rev Lett 2024;132:101801
BESIII Collaboration, Ablikim M, et al. Investigation of the∆I = 1/2 rule and test of CP symmetry through the measurement of decay asymmetry parameters in Ξ− decays, Phys Rev Lett 2024;132:101801
2024
-
[23]
Tests of CP symmetry in entan- gled Ξ0 ¯Ξ0 pairs, Phys Rev D 2023;108:L031106
BESIII Collaboration, Ablikim M, et al. Tests of CP symmetry in entan- gled Ξ0 ¯Ξ0 pairs, Phys Rev D 2023;108:L031106
2023
-
[24]
Measurement of Λ0 b, Λ+ c , and Λ decay parameters using Λ0 b→ Λ+ c h− decays, Phys Rev Lett 2024;133:261804
LHCb Collaboration, Aaij R, et al. Measurement of Λ0 b, Λ+ c , and Λ decay parameters using Λ0 b→ Λ+ c h− decays, Phys Rev Lett 2024;133:261804
2024
-
[25]
Large CP violation in charmed baryon decays, arXiv: 2404.19166, 2024
He XG, Liu CW. Large CP violation in charmed baryon decays, arXiv: 2404.19166, 2024. 3
2024 arXiv
Reviewed August 11, 2026 · model on record in the stance chip above.
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