Measurement of the time-dependent CP asymmetries in $B_s^0\to J\mathrm{/}\psi K_{\mathrm{S}}^0$

The first measurement of decay-time-dependent CP asymmetries in the decay $B_s^0\to J\mathrm{/}\psi K_{\mathrm{S}}^0$ and an updated measurement of the ratio of branching fractions $$\mathcal{B}$(B_s^0\rightarrow J/\psi K_{\rm S}^0)/$\mathcal{B}$(B_d^0\rightarrow J/\psi K_{\rm S}^0)$} are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb${}^{-1}$ of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The results on the CP asymmetries are $A_{\Delta\Gamma}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = 0.49_{-0.65}^{+0.77}(stat) \pm 0.06(syst)$,$C_{\rm dir}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = -0.28 \pm 0.41(stat) \pm 0.08(syst)$and$S_{\rm mix}(B_s^0\rightarrow J/\psi K_{\rm S}^0) = -0.08 \pm 0.40(stat) \pm 0.08(syst)$\mathrm{.}Theratio$$\mathcal{B}$(B_s^0\rightarrow J/\psi K_{\rm S}^0)/$\mathcal{B}$(B_d^0\rightarrow J/\psi K_{\rm S}^0)$ismeasuredtobe$0.0431 \pm 0.0017(stat) \pm 0.0012(syst) \pm 0.0025(f_s/f_d)$, where the last uncertainty is due to the knowledge of the $B_s^0$ and $B_d^0$ production fractions.