Observation of B mesons and measurement of the B /b yield ratio in PbPb collisions at TeV

The B${}_{s}^{0}$ and B$^{+}$ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb$^{−1}$. The mesons are reconstructed in the exclusive decay channels B${}_{s}{}^{0}\to \text{J}/\psi \left({\mu }^{+}{\mu }^{-}\right)\varphi \left({\text{K}}^{+}{\text{K}}^{-}\right)$ and B${}^{+}\to \text{J}/\psi \left({\mu }^{+}{\mu }^{-}\right){\text{K}}^{+}$, in the transverse momentum range 7–50GeV/c and absolute rapidity 0–2.4. The B${}_{s}^{0}$ meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of B${}_{s}^{0}$ and B$^{+}$ is measured and compared to theoretical models that include quark recombination effects.