Bs semileptonic asymmetry at LHCb

When neutral $B^{0}_{s,d}$ mesons evolve in time they can change into their own antiparticles. In this mixing process CP symmetry is not necessarily conserved, as the probability for a $B^{0}$ meson to change into a $\bar{B}^{0}$ meson can be different from the probability for the reverse process. The CP violation in the $B^{0}_{s}$ system as measured using semileptonic decays, defined as $a^{s}_{sl}$, is very small according to the Standard Model. However, earlier measurements of the semileptonic mixing asymmetry in both the $B_s^{0}$ and $B_d^{0}$ systems have shown a $3 \sigma$ deviation with respect to the Standard Model value. A measurement of $a^{s}_{sl}$ performed using $1 \text{fb}^{-1}$ of data collected at the LHCb detector is presented, together with an outlook to the updated $3 \text{fb}^{-1}$ result.