Top-quark pair production in p+Pb collisions in the ATLAS experiment

Measurements of top-quark pairs in heavy-ion collisions are expected to provide novel probes of nuclear parton distribution functions at high Bjorken-x values, which are difficult to access experimentally using other available probes. In this report, the observation of top-quark pair production in proton-lead collisions at the centre-of-mass energy of 8.16 TeV in the ATLAS experiment at the LHC is discussed. Top-quark pair production is measured in the lepton+jets and the di-lepton channels, with a significance well above 5 standard deviations in each channel separately. The nuclear modification factor RpA is also measured for the first time for the top-quark pair process.