$$\varvec{B_c}$$ to A transition form factors and semileptonic decays in self-consistent covariant light-front approach

Abstract

We present a comprehensive analysis of the semileptonic weak decays of $$B_c$$ B c meson decaying to axial-vector (A) mesons for bottom-conserving and bottom-changing decay modes. We employ self-consistent covariant light-front quark model (CLF QM) that uses type-II correspondence to eliminate inconsistencies in the traditional type-I CLF QM. As a fresh attempt, we test the self-consistency in CLF QM through type-II correspondence for $$B_c \rightarrow A$$ B c → A meson transition form factors. We establish that in type-II correspondence the form factors for longitudinal and transverse polarization states are numerically equal and are free from zero-mode contributions, which confirms the self-consistency of type-II correspondence for $$B_c \rightarrow A$$ B c → A transition form factors. Furthermore, we ascertain that the problems of inconsistency and violation of covariance of CLF QM within the type-I correspondence are resolved in type-II correspondence for $$B_c \rightarrow A$$ B c → A transitions. We thoroughly investigate the effects of self-consistency between type-I and type-II schemes using a comparative analysis. In this investigation, we employ a direct calculation approach to determine the form factors within the space-like region. Subsequently, we employ a vector meson dominance (VMD)-inspired three-parameter form to extrapolate these form factors into the physically accessible region. This enables us to study the $$q^2$$ q 2 dependence of the form factors in weak hadronic currents for the whole accessible kinematic range for both bottom-conserving as well as bottom-changing transitions. In addition, we extend our analysis to predict the branching ratios of the semileptonic weak decays of $$B_c$$ B c meson involving axial-vector meson in the final state to quantify the effects of self-consistency in these decays that were not studied before. We evaluate the lepton mass effect on these branching ratios and various other important physical observables, such as forward-backward asymmetries, lepton-side convexity parameter, asymmetry parameter, and longitudinal polarization asymmetries and fractions. Finally, we obtain the lepton flavor universality ratios for various decays.