Phenomenological studies on neutral B-meson decays into $$J/\psi f_1$$ and $$\eta _c f_1$$

AbstractThe axial-vector mesons $$f_1(1285)$$ f 1 ( 1285 ) and $$f_1(1420)$$ f 1 ( 1420 ) are particularly viewed as the mixtures of flavor states $$f_n$$ f n and $$f_s$$ f s with mixing angle $$\varphi $$ φ . In order to determine this angle, we study the $$B_{d,s}^0\rightarrow J/\psi f_1(1285,1420)$$ B d , s 0 → J / ψ f 1 ( 1285 , 1420 ) and $$B_{d,s}^0\rightarrow \eta _c f_1(1285,1420)$$ B d , s 0 → η c f 1 ( 1285 , 1420 ) decays in perturbative QCD (PQCD) approach, including the effects of vertex corrections, nonfactorizable diagrams and penguin operators. Not only the branching fractions, but also the direct CP asymmetries and the polarization fractions are calculated. It is found that the branching fractions of these decays are large enough to be measured in the running LHCb and Belle-II experiments. Moreover, in comparison with the observed $${\mathcal {B}}(B_{d,s}^0 \rightarrow J/\psi f_1(1285))$$ B ( B d , s 0 → J / ψ f 1 ( 1285 ) ) , $$B_s^0 \rightarrow (J/\psi , \eta _c) f_1(1420)$$ B s 0 → ( J / ψ , η c ) f 1 ( 1420 ) decays have large branching fractions, which could be measured promisingly through $$f_1(1420) \rightarrow K_S^0 K^\pm \pi ^\mp $$ f 1 ( 1420 ) → K S 0 K ± π ∓ in experiments. We also propose several ratios that could be used to further constrain the absolute value of the mixing angle $$\varphi $$ φ , but its sign cannot be determined yet in these decays. The direct CP asymmetries of these decays indicate the penguin pollution in the $$B_d^0 \rightarrow (J/\psi , \eta _c) f_1$$ B d 0 → ( J / ψ , η c ) f 1 decays cannot be neglected. We acknowledge that there are large theoretical uncertainties arising from the distribution amplitudes of axial-vector mesons and charmonium states, and more precise nonperturbative parameters are called. The comparisons between our results and future experimental data would help us to understand the nature of $$f_1$$ f 1 states and to test the PQCD approach.