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Assessment of the a2(1320) tensor-meson contribution to η/η′→π0γγ decays

Rafel Escribano1,2,*, Sergi Gonzàlez-Solís3,4,†, and Emilio Royo2,5,‡

  • *Contact author: rescriba@ifae.es
  • †Contact author: sergig@icc.ub.edu
  • ‡Contact author: emilio.royocarratala@uchceu.es
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Phys. Rev. D 112, 114009 – Published 3 December, 2025

DOI: https://doi.org/10.1103/y661-zt9k

Abstract

In light of the recent measurement of the η→π0γγ decay by the KLOE-2 Collaboration, a previous analysis including vector- and scalar-meson exchange contributions using the vector meson dominance and linear sigma model frameworks, respectively, is extended in the present study to incorporate the effects of the a2(1320) tensor meson within a chiral context. Although the individual contribution of the a2 is negligible, its destructive interference with the vector-meson resonances is found to be significant, representing approximately 18% of the total signal and substantially affecting the diphoton invariant-mass distribution, especially at low mγγ2 values. The total decay rate is calculated to be Γ(η→π0γγ)=0.154(22)  eV, which corresponds to a branching ratio of BR(η→π0γγ)=1.17(17)×10−4. This result is approximately 5σ below the reported value of the particle data group, 2.55(22)×10−4, while it is in very good agreement with the KLOE-2 measurement, 0.98(11stat)(14syst)×10−4. In contrast, the total contribution of the a2 is found to be negligible in η′→π0γγ, as this process is completely dominated by the exchange of an on-shell ω vector resonance.

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References (39)

  1. S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024).
  2. M. N. Achasov et al., Nucl. Phys. B600, 3 (2001).
  3. L. Gan, B. Kubis, E. Passemar, and S. Tulin, Phys. Rep. 945, 1 (2022).
  4. D. Alde et al. (Serpukhov-Brussels-Annecy(LAPP) Collaboration and Soviet-CERN Collaboration), Z. Phys. C 25, 225 (1984).
  5. B. M. K. Nefkens et al. (A2 at MAMI Collaboration), Phys. Rev. C 90, 025206 (2014).
  6. S. Prakhov et al., Phys. Rev. C 78, 015206 (2008).
  7. D. Babusci et al. (KLOE-2 Collaboration), arXiv:2505.09285.
  8. B. Di Micco et al. (KLOE Collaboration), Acta Phys. Slovaca 56, 403 (2006).
  9. L. Ametller, J. Bijnens, A. Bramon, and F. Cornet, Phys. Lett. B 276, 185 (1992).
  10. P. Ko, Phys. Lett. B 349, 555 (1995).
  11. E. Oset, J. R. Pelaez, and L. Roca, Phys. Rev. D 67, 073013 (2003).
  12. E. Oset, J. R. Pelaez, and L. Roca, Phys. Rev. D 77, 073001 (2008).
  13. R. Escribano, S. Gonzàlez-Solís, R. Jora, and E. Royo, Phys. Rev. D 102, 034026 (2020).
  14. I. Danilkin, O. Deineka, and M. Vanderhaeghen, Phys. Rev. D 96, 114018 (2017).
  15. J. Lu and B. Moussallam, Eur. Phys. J. C 80, 436 (2020).
  16. S. Uehara et al. (Belle Collaboration), Phys. Rev. D 80, 032001 (2009).
  17. The JLab Eta Factory (JEF) Experiment, Update to the JEF proposal (PR12-14-004),” https://www.jlab.org/exp_prog/proposals/17/C12-14-004.pdf.
  18. R. Escribano and E. Royo, Eur. Phys. J. C 80, 1190 (2020); 81, 140(E) (2021); 82, 743(E) (2022).
  19. R. Escribano, S. Gonzàlez-Solís, and E. Royo, Phys. Rev. D 106, 114007 (2022).
  20. A. Bramon, A. Grau, and G. Pancheri, Phys. Lett. B 344, 240 (1995).
  21. J. Prades, Z. Phys. C 63, 491 (1994); 11, 571(E) (1999).
  22. R. Escribano and E. Royo, Phys. Lett. B 807, 135534 (2020).
  23. A. Bramon, R. Escribano, and M. D. Scadron, Eur. Phys. J. C 7, 271 (1999).
  24. G. Ecker and C. Zauner, Eur. Phys. J. C 52, 315 (2007).
  25. F. Ambrosino et al. (KLOE Collaboration), Phys. Lett. B 648, 267 (2007).
  26. S. Bellucci, J. Gasser, and M. E. Sainio, Nucl. Phys. B423, 80 (1994); B431, 413(E) (1994).
  27. C. Chen, N.-Q. Cheng, L.-W. Yan, C.-G. Duan, and Z.-H. Guo, Phys. Rev. D 108, 014002 (2023).
  28. F. Giacosa, T. Gutsche, V. E. Lyubovitskij, and A. Faessler, Phys. Rev. D 72, 114021 (2005).
  29. D. Drechsel, M. Gorchtein, B. Pasquini, and M. Vanderhaeghen, Phys. Rev. C 61, 015204 (1999).
  30. B. Kubis and J. Plenter, Eur. Phys. J. C 75, 283 (2015).
  31. J. M. Blatt and V. F. Weisskopf, Theoretical Nuclear Physics (Springer, New York, 1952).
  32. J. Elam et al. (REDTOP Collaboration), arXiv:2203.07651.
  33. M. Achasov et al., Front. Phys. (Beijing) 19, 14701 (2024).
  34. X. Chen et al., Nucl. Sci. Tech. 36, 137 (2025).
  35. M. Ablikim et al. (BESIII Collaboration), Phys. Rev. D 96, 012005 (2017).
  36. H. Schäfer, M. Zanke, Y. Korte, and B. Kubis, Phys. Rev. D 108, 074025 (2023).
  37. S. Tulin, Phys. Rev. D 89, 114008 (2014).
  38. Y. Balytskyi, Phys. Lett. B 838, 137668 (2023).
  39. C. Delaunay, T. Kitahara, Y. Soreq, and J. Zupan, J. High Energy Phys. 10 (2025) 222.

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Phys. Rev. D 112, 114009– Published 3 December, 2025
  • Received 7 October 2025
  • Accepted 18 November 2025
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