Form factor for Dalitz decays from J/ψ to light pseudoscalars

We calculate the form factor M(q^2) for the Dalitz decay J/ψ→γ^*(q^2)η_(N_f=1) with η_(N_f) being the SU(N_f) flavor singlet pseudoscalar meson. The difference among the partial widths Γ(J/ψ→γη_(N_f)) at different N_f can be attributed in part to the 𝐔_A(1) anomaly that induces a N_f scaling. M(q^2)'s in N_f=1,2 are both well described by the single pole model M(q^2)=M(0)/(1-q^2/Λ^2). Combined with the known experimental results of the Dalitz decays J/ψ→ Pe^+e^-, the pseudoscalar mass m_P dependence of the pole parameter Λ is approximated by Λ(m_P^2)=Λ_1(1-m_P^2/Λ_2^2) with Λ_1=2.64(4) GeV and Λ_2=2.97(33) GeV. These results provide inputs for future theoretical and experimental studies on the Dalitz decays J/ψ→ Pe^+e^-.