Speaker
Description
We present a first-principles lattice QCD calculation of the radiative transitions of charmonium states to the light pseudoscalar mesons $\eta$ and $\eta'$. We extract the relevant transition form factors as a function of photon virtuality and connect the timelike region accessible through Dalitz decays to the real-photon point. A recurring challenge in these calculations is the appearance of the $\eta'$ as an excited state of the pseudoscalar isoscalar tower. We address this through variationally optimised operators for both the charmonium and light-quark mesons. To manage the noisy disconected process we use a dedicated correlator-averaging strategy that yields clean signals at a dense set of kinematic points. We illustrate the methodology and discuss results across several channels, highlighting the expected difference in $\eta'$ and $\eta$ production and the prospects for extending these techniques to further charmonium transitions and to processes involving genuine light-meson resonances.