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Negative- $Σ \bar{Σ}$ angular-parameter puzzle in $J / ψ$ and $ψ (2 S)$ decays

Chao-Qiang Geng^*, Xiang-Nan Jin^†, and Chia-Wei Liu^‡

School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310024, China

^*Contact author: cqgeng@ucas.ac.cn
^†Contact author: xnjin@ucas.ac.cn
^‡Contact author: chiaweiliu@ucas.ac.cn

Phys. Rev. D 114, 074034 – Published 16 October, 2026

DOI: https://doi.org/10.1103/39xh-tvhx

Abstract

Experimental measurements of $J / ψ$ and $ψ (2 S)$ decays to octet baryon pairs reveal a negative- $Σ \bar{Σ}$ puzzle in the angular distributions, $α_{Σ}^{J / ψ} < 0$ , whereas the other measured $J / ψ$ octet channels and the corresponding $ψ (2 S)$ channels have positive angular parameters. We show that an $SU (3)_{F}$ -exact singlet description is strongly disfavored in a $χ^{2}$ fit, giving $χ^{2} ≃ 10^{5}$ . By contrast, a reduced scenario in which a common final-state interaction mixes the $S$ - and $D$ -wave amplitudes gives $χ^{2} = 4.21$ for the 22 isospin-reduced inputs and two nominal degrees of freedom. We find that the negative- $Σ \bar{Σ}$ puzzle can be reproduced with direct-production $SU (3)_{F}$ breaking at the 40% level. This is larger than the conventional quark-mass expectation of about 30%, but numerically smaller than the order-one channel variation suggested by the experimental data. The sizable observable effect is amplified by $SU (3)_{F}$ -breaking rescattering paths involving S–D mixing. These paths feed the much larger D-wave source into the final $SU (3)_{F}$ -breaking S-wave amplitude. The largest remaining pull comes from the $ψ (2 S) \to N \bar{N}$ angular input, motivating a renewed experimental check of $ψ (2 S) \to n \bar{n}$ .

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Phys. Rev. D 114, 074034– Published 16 October, 2026

Vol. 114, Iss. 7 — 1 October 2026

Received 23 July 2026
Accepted 25 September 2026

DOI: https://doi.org/10.1103/39xh-tvhx

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Negative- $Σ \bar{Σ}$ angular-parameter puzzle in $J / ψ$ and $ψ (2 S)$ decays

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Negative-ΣΣ¯ angular-parameter puzzle in J/ψ and ψ(2S) decays

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Negative- $Σ \bar{Σ}$ angular-parameter puzzle in $J / ψ$ and $ψ (2 S)$ decays