Study of form factors and observables in $$ {B}_c^{-} $$ → $$ {\overline{D}}^{\left(\ast \right)0}{\ell}^{-}{\overline{ u}}_{\ell } $$ and $$ {B}_c^{-} $$ → D(∗)−ℓ+ℓ− decays

A bstract We investigate the decays $$ {B}_c^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> → $$ {\overline{D}}^{\left(\ast \right)0}{\ell}^{-}{\overline{\nu}}_{\ell } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mover> <mml:mi>D</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mrow> <mml:mfenced> <mml:mo>∗</mml:mo> </mml:mfenced> <mml:mn>0</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mi>ℓ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>ℓ</mml:mi> </mml:msub> </mml:math> and $$ {B}_c^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> → D (∗)− ℓ + ℓ − within the Standard Model (SM), employing perturbative QCD (pQCD) form factors that are sensitive to the wave functions of B c and D (∗) mesons. Using lattice QCD inputs for B → D (∗) and B c → D transitions, we extract the shape parameters of the meson wave functions and estimate the q 2 -dependence of B c → 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 $$ {B}_c^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> → D ∗− (→ D 0 π − ) ℓ + ℓ − , providing SM expectations for several angular observables.