Radiative transitions of hybrid mesons

Eric Swanson (Co-PI, University of Pittsburgh) and Shahriyar Jafarzade (ExoHad postdoc, University of Pittsburgh) have investigated how hybrid mesons (particles containing a quark-antiquark pair and an excited gluonic field) decay into ordinary mesons by emitting a photon. Their new study examines the lowest charmonium-hybrid multiplet using a constituent-gluon model based on Coulomb-gauge QCD.

A central finding is the importance of a previously overlooked leading “seagull” interaction, which couples gluon absorption and photon emission at a single vertex. Including this mechanism and subleading spin-dependent interactions, the authors calculate a number of radiative transitions and identify distinctive decay patterns that can test the internal structure of hybrids.

Comparisons with lattice QCD reveal both agreement and an unresolved puzzle. The vector-hybrid transitions to $\eta_c\gamma$ and $\chi_{c0}\gamma$ are compatible with available lattice constraints, while the predicted $\eta_{c1}\to J/\psi\gamma$ rate is substantially smaller than lattice estimates. These results motivate further lattice calculations and provide a foundation for extending the approach to light hybrids relevant to the GlueX program at Jefferson Lab.

Papers: arXiv:2610.22088