A Phenomenological Study of Semileptonic $B^+$ and $B_s^0$ Decays into Axial-Vector Mesons $\big(D_1(2420),\, D_1^\prime(2430),\, D_{s1}(2460),\, \text{and } D_{s1}^\prime(2536)\big)$ within the Standard Model

We study semileptonic $B$ meson decays $B^+ \to D_1^{(\prime)}\ell^+ν_\ell$ and $B_s^0 \to D_{s1}^{-(\prime)}\ell^+ν_\ell$, where $\ell=μ,τ$. The final state axial vector mesons are treated as mixtures of the heavy quark basis states with light degree of freedom angular momenta $j_\ell=1/2$ and $j_\