Observation of η′ → μ+μ−γ decay

Light Meson Decays at BESIII

“…predictions. The uncertainty of the η transition form factor slope is in good agreement the best determination in the space-like region from the CELLO collaboration b η = (1.60 ± 0.16) GeV −2 [28], and improves the previous determination of the slope in the time-like region b η = (1.7 ± 0.4) GeV −2 [27,29].…”

Observation of the Dalitz decayη′→γe+e−

“…The slope of the TFF corresponds to ð1.60 AE 0.17ðstatÞ AE 0.08ðsysÞÞ GeV −2 and agrees within errors with the VMD model predictions. The uncertainty of the η 0 transition form-factor slope matches the best determination in the spacelike region from the CELLO Collaboration b η 0 ¼ ð1.60 AE 0.16Þ GeV −2 [30], and improves the previous determination of the slope in the timelike region b η 0 ¼ ð1.7 AE 0.4Þ GeV −2 [1,8]. The η 0 form factor is determined by both universal π þ π − rescattering and a reaction specific part, with the latter contributing about 20% to the form-factor slope [14].…”

“…To a first approximation, Λ ≈ M ρ ≈ 0.7 GeV and γ ≈ Γ ρ ≈ 0.12 GeV. For the η 0 Dalitz decay, only the process η 0 → γμ þ μ − has been observed and the slope of the form factor was measured to be b η 0 ¼ ð1.7 AE 0.4Þ GeV −2 [1,8]. To date, the process η 0 → γe þ e − has not been observed yet.…”

Spacelike and timelike form factors for the (π0,η,η′)→Choi1, Ryu2, Ji3 2017Phys. Rev. D230100View full textAdd to dashboardCite

“…which correspond to Λ η = 688 +5 −6 MeV and Λ η = 760 +8 −7 MeV for φ = 37 −5 • +5 , respectively. Our results for the slope parameters for η and η TFFs are consistent with the available experimental data within the error bars: Λ −2 η = (1.95 ± 0.22) GeV −2 [9] and (1.95 ± 0.25) GeV −2 [11] for η TFF, and Λ −2 η = (1.60 ± 0.16) GeV −2 [6], (1.6 ± 0.25) GeV −2 [14], and (1.7 ± 0.4) GeV −2 [101] for η TFF, respectively. We also should note that the ratio of Λ η to Λ η is insensitive to the mixing angle, i.e.…”