Study of Form Factors and Observables in $B_c^- \rightarrow D_{s}^{*-}\ell^+\ell^-$ and $B_c^- \rightarrow D_{s}^{*-}\nu\bar{\nu}$ decays

TL;DR

This paper analyzes rare $B_c$ meson decays into $D_s^{(*)}$ and leptons or neutrinos, using QCD form factors and lattice inputs to predict observables and perform angular analyses within the Standard Model.

Contribution

It provides new predictions for decay rates and angular observables in $B_c$ decays, utilizing form factors derived from lattice QCD and heavy-quark symmetry.

Findings

Predicted branching ratios for $B_c$ decays.

Standard Model predictions for angular observables.

Analysis of form factors and their $q^2$ dependence.

Abstract

We investigate the decays $B_c^- \rightarrow D_{s}^{(*)-}\ell^+\ell^-$ and $B_c^- \rightarrow D_{s}^{(*)-}\nu\bar{\nu}$ within the Standard Model (SM), employing perturbative QCD form factors that are sensitive to the wave functions of $B_c$ and $D_{s}^{(*)}$ mesons. We determine the shape parameters of these mesons and the $B_c \to D_s^{(*)}$ form factors at $q^2 = 0$ from available lattice QCD inputs for $B_s \to D_s^{(*)}$ and $B_c \to D_s$ transitions. To obtain the $q^2$ dependence of the $B_c \to D_s^*$ form factors, we employ heavy-quark spin symmetry and an appropriate parametrisation scheme over the allowed $q^2$ region. Based on these inputs, we present predictions for branching ratios and lepton-flavour-sensitive observables. Furthermore, we perform a detailed angular analysis of the cascade decay $B_c^- \to D_s^{*-}(\to D_s^- \pi^0)\,\ell^+\ell^-$, providing Standard Model predictions for several angular observables.