Is there gluonium in the η^′? The flavour structure of η and η^′ mixing in radiative V→ Pγ and P→ Vγ decays

@misc{escribano2026there,
  title = {{Is there gluonium in the $η^\prime$? The flavour structure of $η$ and $η^\prime$ mixing in radiative $V\to Pγ$ and $P\to Vγ$ decays}},
  author = {Rafel Escribano and Emilio Royo},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.25216},
  eprint = {2610.25216},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.25216},
}

TY  - UNPB
TI  - Is there gluonium in the η^′? The flavour structure of η and η^′ mixing in radiative V→ Pγ and P→ Vγ decays
AU  - Rafel Escribano
AU  - Emilio Royo
PY  - 2026
DA  - 2026/10/18
PB  - arXiv
DO  - 10.48550/arxiv.2610.25216
UR  - https://arxiv.org/abs/2610.25216
AB  - Radiative V→ Pγ and P→ Vγ decays are conventionally described using constituent-quark mass differences and phenomenological wavefunction-overlap factors as sources of flavour-symmetry breaking. We investigate whether the overlap factors can instead be understood as the effect of mixing of the η and η^′ with an additional pseudoscalar state, described by an SO(4) rotation among four basis states. A global fit to current data yields a significantly better description than the corresponding three-state limit without overlap factors, while preserving the established η-η^′ and vector-meson mixing angles, and shows that the additional state mixes predominantly with the non-strange component. The conventional overlap-factor description is recovered exactly as the special case in which this mixing is purely non-strange. The non-strange pattern disfavours both a flavour-singlet admixture, as expected from mixing with a pseudoscalar glueball, and the gluonium scenario considered in previous analyses. Radiative decays therefore provide no compelling evidence for gluonium in the η^′, and the overlap factors are better interpreted in terms of a radially excited non-strange state.
ER  -