Observation of the ${\rm B_c^+}$ meson in PbPb and pp collisions at $\sqrt{s_{\rm NN}}=5.02~\mathrm{TeV}$

The ${\rm B_c^+}$ meson is observed with the CMS detector in proton-proton and lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}=5.02~\mathrm{TeV}$, via the ${\rm B_c^+} \rightarrow ({\rm J}/\psi \rightarrow \mu^+ \mu^-) \mu^+ \nu_\mu$ decay. Its cross section and nuclear modification factor are measured in two bins of the trimuon transverse momentum, and in two ranges of collision centrality. As the ${\rm B_c^+}$ is the only meson containing two different flavored heavy quarks, it provides a unique bridge between charmonia, bottomonia, and open heavy mesons. The insights gained from these results will further the understanding of the interplay of suppression and enhancement mechanisms in the production of heavy mesons in the hot and dense matter created in heavy ion collisions.