Enhancement of direct CP asymmetry in Z' models

We consider CP-violating Z' models to account for the anomalies in b -> sll decays. Using the updated constraints from lepton flavor universality violating ratios, b. s mu mu CP-conserving and CP-violating observables, B-s - (B) over bars mixing and neutrino trident we obtain the favored parameter space of two classes of Z' models generating the new physics scenarios with Re [C-9(mu NP)] < 0 and [C-9(mu NP) = -C-10(mu NP), C-9(eNP) = -C-10(eNP)]. We study the predictions of direct CP asymmetry A(CP) in B+ -> K+mu mu decays and CP asymmetric angular observables in these models. The favored 1 sigma parameter space of Z' models generating scenario Re[C-9(mu NP)] < 0 allows for an enhancement in the integrated A(CP) in q(2) = [8, 9] GeV2 bin up to +/- 25%, while the [C-9(mu NP) = -C-10(mu NP), C-9(eNP) = -C-10(eNP)] scenario allows only positive values of A(CP). However, these A(CP) values flip sign depending on the choice of J/psi phase, hence distinguishing these two Z' models through a measurement in this bin requires a more reliable determination of the J/psi phase. The prediction of A(CP) in the q(2) = [16, 17] GeV2 bin are promising as they allow for an enhancement only in the positive direction for [C-9(mu NP) = -C-10 mu NP, C-9(eNP) = -C-10(eNP)] scenario, irrespective of the choice of strong phase, while both positive and negative values are allowed for the scenario Re[C-9(mu NP)]. We also find that a future more precise measurement of CP-asymmetric angular observables A(8) and A(9) in the low-q(2) bins can provide distinguishing signatures of these two Z' models and help constrain new physics CP-violating phases.