Observation of the decay J/ψ →e+e-η (1405) with η (1405) →π0f0 (980)

Using a data sample of (10087±44)×106 J/ψ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process J/ψ→e+e-η(1405) is observed via the decay η(1405)→π0f0(980), f0(980)→π+π-, with a significance of about 9.8σ. The branching fraction of this decay is measured to be B(J/ψ→e+e-η(1405)→e+e-π0f0(980)→e+e-π0π+π-)=(2.04±0.20(stat)±0.08(syst))×10-7. The branching fraction ratio B(J/ψ→e+e-η(1405))/B(J/ψ→γη(1405)) is determined to be (1.36±0.17(stat)±0.06(syst))×10-2. Furthermore, an e+e- invariant mass dependent transition form factor of J/ψ→e+e-η(1405) is presented for the first time. The obtained result provides input for different theoretical models and is valuable for the improved understanding the intrinsic structure of the η(1405) meson. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.