Observation of $\mathrm{B^{0}_{s}}$ mesons and measurement of the $\mathrm{B^{0}_{s}}/\mathrm{B^{+}}$ yield ratio in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV
A. Tumasyan, R. Erbacher, C. A. Carrillo Montoya, W. Carvalho et autres