Bd,s0 → f1f1 decays with f1 (1285) - f1 (1420) mixing in the perturbative QCD approach

We investigate the B-d,s(0) -> f(1)f(1) decays in the framework of perturbative QCD (PQCD) approach with a referenced value Qf(1) similar to 24 degrees. Here, f(1) denotes the axial-vector mesons f(1) (1285) and f(1) (1420) with mixing angle Qf(1) in the quark-flavor basis. The observables such as branching ratios, direct CP violations, and polarization fractions of the B-0 -> f(1)f(1) decays are predicted for the first time. We find that (i) the almost pure penguin modes B-0 -> f(1)f(1) have large branching ratios in the order of 10(-6) similar to 10(-5) due to the CabibboKobayashi-Maskawa enhancement and generally constructive interferences between the amplitudes of B-s(0) -> f(n)f(s) and B-s(0) -> f(s)f(s) with f(n) and f(s) being the quark-flavor states of f(1) mesons. (ii) The observables receive important contributions from the weak annihilation diagrams in the PQCD approach. In particular, without the annihilation contributions, the B-s(0) -> f(1) (1420) f(1) (1420) branching ratio will decrease about 81% and its longitudinal polarization fraction will reduce around 43%. And (iii) the dependence of the B-d,s(0) -> f(1)f(1) decay rates on Qf(1) exhibits some interesting line shapes, whose confirmations would be helpful to constrain the determination of Qf(1) inversely. All the PQCD predictions await for the (near) future examinations at Large Hadron Collider beauty and/or Belle-II experiments to further understand the properties of the axial-vector mesons and the perturbative dynamics released from the considered decay modes.