Updated study of the ηc and ηc′ decays into light vector mesons

We re-investigate the exclusive decays of ηc and ηc′ to a pair of light vector mesons, i.e. ηc(ηc′)→VV. The long-distance intermediate meson loop (IML) effects are evaluated as a non-perturbative mechanism in addition to the short-distance cc¯ annihilation contributions. We show that both processes can be reasonably well constrained with the help of the available experimental data. Since ηc and ηc′ are the spin-0 partners of J/ψ and ψ′, respectively, our study is useful for gaining insights into the pQCD helicity selection rule violations in charmonium decays and the long-standing “ρπ puzzle”.