Measurement of the top quark pair production cross section in PbPb collisions at sqrt(s_NN) = 5.36 TeV

The inclusive cross section for top quark pair (t¯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 t¯t production cross section, σt¯t=3.42+0.54−0.51(stat)+0.50−0.43(syst) μb, 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 (σDY) for dilepton masses above 10 GeV and the ratio of t¯t to DY cross sections (Rt¯t/DY) are found to be compatible with the NNLO predictions. The observables σt¯t, σDY, and Rt¯t/DY 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.