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Isospin strikes back.

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Title: Isospin strikes back.
Authors: Rosini, Francesco1 (AUTHOR) francesco.rosini@pg.infn.it, Pacetti, Simone1 (AUTHOR) simone.pacetti@unipg.it
Source: European Physical Journal C -- Particles & Fields. Mar2025, Vol. 85 Issue 3, p1-6. 6p.
Subjects: Particle physics, Born approximation, Isobaric spin, Photons, Hypothesis
Abstract: Assuming isospin conservation, the decay of a c c ¯ vector meson into the Λ Σ ¯ 0 + c. c. final state is purely electromagnetic. At the leading order, the c c ¯ vector meson first converts into a virtual photon that, then produces the Λ Σ ¯ 0 + c. c. final state. Moreover, such a mechanism, i.e., the virtual photon coupling to Λ Σ ¯ 0 + c. c. , is the sole intermediate process through which, in Born approximation, the reaction e + e - → Λ Σ ¯ 0 + c. c. does proceed. It follows that any significant difference between the amplitudes of the processes c c ¯ → Λ Σ ¯ 0 + c. c. and e + e - → Λ Σ ¯ 0 + c. c. at the c c ¯ mass must be ascribed to an isospin-violating contribution in the c c ¯ decay. In Ferroli et al. (Eur Phys J C 80: 903, 2020) we studied the decay of the ψ (2 S) vector meson into Λ Σ ¯ 0 + c. c. and, on the light of the large branching fraction BR 18 (ψ (2 S) → Λ Σ ¯ 0 + c. c.) = (1.23 ± 0.24) × 10 - 5 , published in the 2018 edition of the Review of Particle Physics (Tanabashi et al. in Phys Rev D 98: 030001, 2018), we claimed either the presence of a significant isospin-violating contribution or, with a lesser emphasis, a "not complete reliability of the only available datum". In any case, we propose a new measurement. Apparently, our second and considered less serious hypothesis was the right one, indeed the branching fraction published in the 2024 edition of the Review of Particle Physics (Navas et al. in Phys Rev D 110: 030001, 2024) is BR (ψ (2 S) → Λ Σ ¯ 0 + c. c.) = (1.6 ± 0.7) × 10 - 6 , more than seven times lower with the error that increased from ∼ 20 % to ∼ 45 % . [ABSTRACT FROM AUTHOR]
Copyright of European Physical Journal C -- Particles & Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Isospin strikes back.
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  Data: <searchLink fieldCode="AR" term="%22Rosini%2C+Francesco%22">Rosini, Francesco</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> francesco.rosini@pg.infn.it</i><br /><searchLink fieldCode="AR" term="%22Pacetti%2C+Simone%22">Pacetti, Simone</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> simone.pacetti@unipg.it</i>
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  Data: <searchLink fieldCode="JN" term="%22European+Physical+Journal+C+--+Particles+%26+Fields%22">European Physical Journal C -- Particles & Fields</searchLink>. Mar2025, Vol. 85 Issue 3, p1-6. 6p.
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  Data: Assuming isospin conservation, the decay of a c c ¯ vector meson into the Λ Σ ¯ 0 + c. c. final state is purely electromagnetic. At the leading order, the c c ¯ vector meson first converts into a virtual photon that, then produces the Λ Σ ¯ 0 + c. c. final state. Moreover, such a mechanism, i.e., the virtual photon coupling to Λ Σ ¯ 0 + c. c. , is the sole intermediate process through which, in Born approximation, the reaction e + e - → Λ Σ ¯ 0 + c. c. does proceed. It follows that any significant difference between the amplitudes of the processes c c ¯ → Λ Σ ¯ 0 + c. c. and e + e - → Λ Σ ¯ 0 + c. c. at the c c ¯ mass must be ascribed to an isospin-violating contribution in the c c ¯ decay. In Ferroli et al. (Eur Phys J C 80: 903, 2020) we studied the decay of the ψ (2 S) vector meson into Λ Σ ¯ 0 + c. c. and, on the light of the large branching fraction BR 18 (ψ (2 S) → Λ Σ ¯ 0 + c. c.) = (1.23 ± 0.24) × 10 - 5 , published in the 2018 edition of the Review of Particle Physics (Tanabashi et al. in Phys Rev D 98: 030001, 2018), we claimed either the presence of a significant isospin-violating contribution or, with a lesser emphasis, a "not complete reliability of the only available datum". In any case, we propose a new measurement. Apparently, our second and considered less serious hypothesis was the right one, indeed the branching fraction published in the 2024 edition of the Review of Particle Physics (Navas et al. in Phys Rev D 110: 030001, 2024) is BR (ψ (2 S) → Λ Σ ¯ 0 + c. c.) = (1.6 ± 0.7) × 10 - 6 , more than seven times lower with the error that increased from ∼ 20 % to ∼ 45 % . [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of European Physical Journal C -- Particles & Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1140/epjc/s10052-025-13976-7
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        Text: English
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      – SubjectFull: Born approximation
        Type: general
      – SubjectFull: Isobaric spin
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      – SubjectFull: Photons
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      – TitleFull: Isospin strikes back.
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            NameFull: Rosini, Francesco
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            – D: 01
              M: 03
              Text: Mar2025
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              Y: 2025
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