Constraints on new physics couplings from $\bar{B}\to D^{\ast }(D\pi )\mathrm{\ell }{\bar{\nu }}_{\mathrm{\ell }}$ angular analysis

The Belle Collaboration has measured the complete set of angular coefficient functions for the decays $\bar{B}\to D^{\ast }(D\pi )\mathrm{\ell }{\bar{\nu }}_{\mathrm{\ell }}$, where $\mathrm{\ell }=e,\mu$, in four bins of the variable $w=\frac{m_B^2+m_{D^{\ast }}^2-q^2}{2m_B{m}_{D^{\ast }}}$, with $q$ the momentum of the lepton pair. In SM this measurement is instrumental in determining the hadronic form factors in the $B\to D^{\ast }$ matrix elements of the SM weak current, thereby refining the measurement of $\mid V_{cb}\mid$. On the other hand, it can be used to assess the impact of possible new physics contributions. I consider an extension of the SM effective Hamiltonian that governs this mode, incorporating the complete set of Lorentz invariant $d=6$ operators compatible with the gauge symmetry of the theory. The measured angular coefficient functions play a pivotal role in constraining the couplings in the generalized effective Hamiltonian.