<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true"><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mrow></mml:mover><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mo>*</mml:mo><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:msup><mml:mo>ℓ</mml:mo><mml:mover accent="true"><mml:mrow><mml:mi>X</mml:mi></mml:…

We calculate the complete differential decay distributions for $B$ meson decays, $\overline{B}\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\ell}\overline{X}$, to a massive right-handed (RH) neutrino in low-energy effective field theory (LEFT) framework. find that RH does not introduce any new angular structures compared massless case, but can cause significant distortions observables. study phenomenology of four-fermion operators permitted by standard model (SMEFT) extended with neutrinos (SMNEFT). show explain positive value difference forward-backward asymmetries, $\mathrm{\ensuremath{\Delta}}{A}_{\mathrm{FB}}\ensuremath{\equiv}{A}_{\mathrm{FB}}^{\ensuremath{\mu}}\ensuremath{-}{A}_{\mathrm{FB}}^{e}$, tentatively inferred from Belle data, must be massive. also make predictions ${q}^{2}$ dependent observables motivate future measurements.