Measurement of differential distribution of $B_{s}\rightarrow D_{s}^{*} \mu \nu_{\mu}$ at LHCb.

Semileptonic decays of the $B_s$ meson play a crucial role in the validation of the Standard Model. They are helpful to constrain the parameters of the CKM matrix, to test the Lepton Flavour Universality, to understand the $CP$ violation and to investigate New Physics effects. The analysis presented here aims to a complete the study of the decay kinematics of the semileptonic decay $B_{s}\rightarrow D_{s}^{*} \mu \nu_{\mu}$, with $D_{s}^{*}\rightarrow D_{s} \gamma$, using data collected by LHCb in Run 2. The decay considered can be fully described by four variables: the invariant mass squared $q^2$ of the lepton pairs and three decay angles, $\theta_l, \theta_d$ and $\chi$, reconstructed from the particles in the final state and the initial $B_s$ flight direction. The full differential distribution in these four kinematic variables is produced, taking into account the detector acceptance, as well as the reconstructed efficiencies and the resolution effects. Then, a fit to this differential distribution is performed using different parametrisations for the $B_{s}\rightarrow D_{s}^{*}$ transition form factors and various kind of New Physics contributions.