Radiative production and decays of the exotic $η_1^\prime(1855)$ and its siblings

Abstract

We study the production of the light $J^{PC}=1^{-+}$ hybrid isoscalars $η_1^\prime(1855)$ and the yet undiscovered $η_1^{hyb}(1660)$ as intermediate states in the radiative decays of the charmonium ($J/ψ$) to two conventional mesons using a flavor symmetric Lagrangian. For this purpose, we use the $J/ψ\toγη_1^\prime(1855)\toγηη^\prime$ process as the reference. We find that some of the decay channels have branching ratios similar to or larger than that of the $γηη^\prime$ channel and are sensitive to the mixing between the hybrid isoscalars. We propose that relatively stable $γηf_1(1285)$ channel be explored for the presence of the light hybrid isoscalar $η_1^{hyb}(1660)$. We also exploit the strong decay channels containing at least one vector meson to study the radiative decays of the whole hybrid nonet $\{π_1(1600),K_1^{hyb}(1750),η_1^{hyb}(1660),η_1'(1855)\}$. We find that the hybrids cannot radiatively decay into the $I=0$ pseudoscalars. Furthermore, the vector decay channels ($(ρ/ω/ϕ)γ$) of the hybrid isoscalars are sensitive to the strangeness content of the hybrids. We also provide estimates for the branching fractions for the radiative production and partial widths for the radiative decays of the hybrids.