Study of Form Factors and Observables in $B_c^- \rightarrow \bar{D}^{(*)0}\ell^-\barν_{\ell}$ and $B_c^- \rightarrow D^{(*)-}\ell^+\ell^-$ decays

Abstract

We investigate the decays $B_c^- \rightarrow \bar{D}^{(*)0}\ell^-\barν_{\ell}$ and $B_c^- \rightarrow D^{(*)-}\ell^+\ell^-$ within the Standard Model (SM), employing perturbative QCD form factors that are sensitive to the wave functions of $B_c$ and $D^{(*)}$ mesons. Using lattice QCD inputs for $B \to D^{(*)}$ and $B_c \to D$ transitions, we extract the shape parameters of the meson wave functions and estimate the $q^2$-dependence of $B_c \to D^*$ form factors via heavy quark spin symmetry. We present predictions for branching fractions, lepton flavor violating observables, and perform a detailed angular analysis of the cascade decay $B_{c}^{-} \to D^{*-}(\to D^{0}π^{-}) \ell^+\ell^-$, providing SM expectations for several angular observables.

Figures (8)

• Figure 4: Kinematics of $B_{c}^{-}\rightarrow D^{*-}(\rightarrow D^{0}\pi^{-}) \ell^{+}\ell^{-}$ four body decay.
• Figure 5: Plots showing the $w$ distribution of $\Sigma_{1}(w)$ and $a_{0}\Sigma_{2}(w)$.
• Figure 6: Plots showing the $q^{2}$ distribution of $B_{c}\rightarrow D$ form factors $F_{+}$ and $F_{0}$. The red markers denote the synthetic data points generated using the BCL parameters supplied by HPQCD.
• Figure 11: The $q^{2}$ dependence of normalized CP averaged angular observables $S_{i}$. The blue and the red plots depict our results for the light lepton and $\tau$ lepton modes respectively and the gray bands denote the region of $J/\psi$ and $\psi(2S)$ resonances.
• Figure 12: The $q^{2}$ dependence of differential branching fractions $d\mathcal{B}/dq^{2}$ of $B_{c}^{-}\rightarrow D^{*-}(\rightarrow D^{0}\pi^{-}) \ell^{+}\ell^{-}$. The first plot depicts our result for the light lepton mode, and the second plot depicts our result for the $\tau$ lepton mode, and the gray bands denote the region of $J/\psi$ and $\psi(2S)$ resonances.