Isovector scalar $a_0(980)$ and $a_0(1450)$ resonances in the $B\to \psi (K\bar{K},\pi \eta )$ decays

We present an analysis of two isovector scalar resonant contributions to the $B$ decays into charmonia plus $K\bar{K}$ or $\pi \eta$ pair in the perturbative QCD approach. The Flatt'{e} model for the $a_0(980)$ resonance and the Breit Wigner formula for the $a_0(1450)$ resonance are adopted to parametrize the timelike form factors in the dimeson distribution amplitudes, which capture the important final state interactions in these processes. The predicted distribution in the $K^{+}{K}^{-}$ invariant mass as well as its integrated branching ratio for the $a_0(980)$ resonance in the $B^0\to J\mathrm{/}\psi K^{+}{K}^{-}$ mode agree well with the current available experimental data. The obtained branching ratio of the quasi-two-body decay $B^0\rightarrow J/\psi a_0(980)(\rightarrow \pi^0\eta)$canreachtheorderof$10^{-6}$, letting the corresponding measurement appear feasible. For the $a_0(1450)$ component, our results could be tested by further experiments in the LHCb and Belle II. We also discuss some theoretical uncertainties in detail in our calculation.