Charmonium radiative transitions to dileptons from lattice QCD: The case of $h_c \to η_c \ell^+\ell^-$ and $χ_{c1} \to J/ψ\,\ell^+\ell^-$

We present a lattice QCD study of dilepton production in charmonium transitions, specifically focusing on the $1^{+-} \to 0^{-+}$ and $1^{++} \to 1^{--}$ processes: $h_c \to η_c \ell^+ \ell^-$ and $χ_{c1} \to J/ψ\ell^+ \ell^-$, where $\ell = e, μ$. The relevant hadronic matrix elements are computed