Speaker
Description
Recent measurements of $B$ meson decays reveal persistent deviations from Standard Model (SM) predictions, particularly in processes involving $ b \to s $ and $ b \to c(u) $ quark-level transitions, suggesting potential signals of new physics (NP). Motivated by the capabilities of current and upcoming high-luminosity $ B $ factories, we investigate the exclusive decay $ B \to a_1(1260) \ell^- \bar{\nu}_\ell $ within a model-independent framework to assess its sensitivity to NP effects. The NP parameters are constrained using the experimentally measured branching fractions of the (semi)leptonic decays $ B \to \ell \bar{\nu} $ and $ B \to (\pi, \rho, \omega) \ell \bar{\nu} $ (with $ \ell = e, \mu, \tau $), which proceed via $ b \to u \ell \bar{\nu} $ transitions. We then perform a detailed angular analysis of the $ B \to a_1(1260) \ell^- \bar{\nu}_\ell $ channel both within the SM and under various NP scenarios. Furthermore, we present theoretical predictions for several observables, including the branching ratio, forward-backward asymmetry, and indicators of lepton flavor universality violation, thereby highlighting the potential of this decay mode as a probe for physics beyond the Standard Model.
