2025/11/29 by Cao, Xiong-Hui, Guo, Feng-Kun, Hanhart, Christoph +1
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2512.00501
Motivated by the discrepancies noted recently between the theoretical predictions of the electromagnetic J/ψ→ π0 γ^* transition form factor and the BESIII data, we reanalyze this transition form factor using the dispersive Khuri-Treiman equations, with final-state interactions in both the direct channel and the crossed channels properly considered. This improved framework incorporates ρ-ω mixing effects. The effect of four-pion states is evaluated through a dispersively improved vector-meson-dominance model. From this information, we propose a two-parameter fit that provides an excellent description of the BESIII data over the broad energy range from 0 to 2.8 GeV. We demonstrate that the ρπ0 decay mode of the J/ψ is dominated by strong interaction, while the ωπ0 mode is dominated by one-photon exchange. From this, we extract the relative phase between the strong and the one-virtual-photon (electromagnetic) modes in hadronic decays of J/ψ as (62 ± 21)∘. This could provide useful information in understanding the long-standing ρπ puzzle in J/ψ decays.