The η/η′→π+π-γ decays within BHLS2 and the muon HVP.

The departure of the latest FNAL experimental average for the muon anomalous magnetic moment a μ = (g μ - 2) / 2 measurements, having increased from 4.2 σ (Abi et al. in Measurement of the positive muon anomalous magnetic moment to 0.46 ppm, , 2021) to 5.0 σ (Muon g-2, D.P. Aguillard et al. in Measurement of the positive muon anomalous magnetic moment to 0.20 ppm, , 2023) with respect to the white paper (WP) consensus (Aoyama et al. in Phys Rep 887:1, , 2020), may indicate a hint for new physics. As the most delicate piece of a μ is its leading-order hadronic vacuum polarization (HVP) part a μ H V P - L O , methods to ascertain its theoretical value are crucial to appropriately interpreting this departure from the measurement. We, therefore, propose to closely examine the dipion spectra from the η / η ′ → π + π - γ decays in the hidden local symmetry (HLS) context using its BHLS 2 broken variant. We thus have at our disposal a framework where the close relationship of the dipion spectra from the η / η ′ and τ decays and of the e + e - → π + π - annihilation can be simultaneously considered. A special focus is given to the high-statistics dipion spectra from the η decay collected by the KLOE/KLOE2 Collaboration and η ′ decay collected by the BESIII Collaboration, and it is shown that the BHLS 2 framework provides a fair account of their dipion spectra. More precisely, it is first proven that a single Omnès representation real polynomial is required, common to both the η and η ′ dipion spectra. Moreover, it is shown that fits involving the η / η ′ / τ dipion spectra, and excluding the e + e - → π + π - annihilation data, allow for a prediction of the pion vector form factor data F π (s) which agrees fairly well with the usual dipion spectra collected in the e + e - → π + π - annihilation channel. Even if more precise η / η ′ / τ dipion spectra would help to be fully conclusive, this confirms the dispersive approach results for a μ H V P - L O and points toward a common non-experimentally dependent origin to this tension with the now well-accepted LQCD result. [ABSTRACT FROM AUTHOR]