Binwise exploration of vector couplings in $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ decays

Abstract

Recent results from the LHCb experiment have confirmed that lepton flavor universality is upheld in flavor-changing neutral current processes, such as $B \to K^{(*)} l^+ l^-$. However, discrepancies remain in the charged current sector, raising questions about the universality of lepton flavors in these processes. To explore this issue, we investigate the decays $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ in different $q^2$ bins, which involve the $b \to c \tau \bar \nu_\tau$ transition. We employ a model-independent approach to analyze potential new physics by fitting both real and complex (axial)vector coefficients to the existing $b \to (u, c) \tau \bar \nu_\tau$ data. Our analysis enables us to calculate the branching ratios and angular distributions for the $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ decays in four different $q^2$ bins. Additionally, we evaluate whether lepton flavor universality is maintained in these charged current decays or if deviations suggest the presence of new physics.