Study of the $B_c \to J/\psi D_s$ and $B_c \to J/\psi D_s^*$ decays with the ATLAS detector

$B_c$ meson. The decays $B_c \to J/\psi D_s$ and $B_c \to J/\psi D_s^*$ provide means to test these theoretical predictions. In the poster we present a measurement of the branching fractions of $B_c \to J/\psi D_s$ and $B_c \to J/\psi D_s^*$ decays normalized to that of $B_c \to J/\psi \pi$ decay performed recently with the ATLAS detector. In addition, we show results of the polarisation measurement in the decay $B_c \to J/\psi D_s^*$.