Measurement of the top quark pair production cross section in PbPb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.36 TeV

The inclusive cross section for top quark pair ($\mathrm{t}\bar{\mathrm{t}}$) production in lead-lead (PbPb) collisions is reported for the first time at a center-of-mass energy per nucleon pair of 5.36 TeV. The analysis uses data corresponding to an integrated luminosity of 1.58 nb${}^{-1}$ collected by the CMS experiment at the CERN LHC in 2023. The $\mathrm{t}\bar{\mathrm{t}}$ production cross section, ${\sigma }_{\mathrm{t}\bar{\mathrm{t}}}$ = 3.42${}_{-0.51}^{+0.54}$(stat)${}_{-0.43}^{+0.50}$(syst) $\mu$b, is measured in dilepton final states using a fit to a multivariate discriminator that combines the decay electron and muon kinematic properties with the multiplicity of bottom quark jets. The result is consistent with perturbative quantum chromodynamics calculations at next-to-next-to-leading order (NNLO) accuracy employing several nuclear parton distribution functions. In addition, the Drell$-$Yan production cross section (${\sigma }_{\text{DY}}$) for dilepton masses above 10 GeV and the ratio of $\mathrm{t}\bar{\mathrm{t}}$ to DY cross sections ($R_{\mathrm{t}\bar{\mathrm{t}}\mathrm{/}\mathrm{D}\mathrm{Y}}$) are found to be compatible with the NNLO predictions. The observables ${\sigma }_{\mathrm{t}\bar{\mathrm{t}}}$, ${\sigma }_{\text{DY}}$, and $R_{\mathrm{t}\bar{\mathrm{t}}\mathrm{/}\mathrm{D}\mathrm{Y}}$ are measured separately for central and semicentral PbPb collisions to investigate for the first time the dependence of top quark production on the collision impact parameter.