Speaker
Description
We perform a general model-independent analysis of $b \to c \tau \bar{\nu}_\tau $ transitions, including measurements of $\mathcal{R}_D$, $\mathcal{R}_{D^*}$, their $q^2$ differential distributions, the recently measured longitudinal $D^*$ polarization $F_L^{D^*}$, and constraints on the $B_c \to \tau \bar{\nu}_\tau$ lifetime. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, assuming CP-invariance and linear electroweak symmetry breaking. The fitted solutions are interpreted in terms of hypothetical new-physics mediators. From the results obtained, we analyze the predictions for additional $b \to c$ observables such as the baryonic transition $\Lambda_b \to \Lambda_c \tau \bar{\nu}_\tau$, the ratio $\mathcal{R}_{J/\psi}$, the forward-backward asymmetry ${\cal A}_\text{FB}^{D^{(*)}}$, the $\tau$ polarization $\mathcal{P}_\tau^{D^{(*)}}$, and the longitudinal $D^*$ polarization $F_L^{D^*}$. At the $1\sigma$ level, one observes clear tensions among the current experimental inputs, independently of any new-physics hypothesis, which suggests that the reported anomalies could be partly driven by underestimated systematic uncertainties.
