Top-quark production in proton–nucleus and nucleus–nucleus collisions at LHC energies and beyond

Single and pair top-quark production in proton–lead (p–Pb) and lead–lead (Pb–Pb) collisions at the CERN Large Hadron Collider (LHC) and Future Circular Collider (FCC) energies, are studied with next-to-leading-order perturbative QCD calculations including nuclear parton distribution functions. At the LHC, the pair-production cross sections amount to σtt¯=3.4 μb in Pb–Pb at sNN=5.5 TeV, and σtt¯=60 nb in p–Pb at sNN=8.8 TeV. At the FCC energies of sNN=39 and 63 TeV, the same cross sections are factors of 90 and 55 times larger respectively. In the leptonic final-state tt¯→W+bW−b¯→bb¯ℓℓνν with ℓ=e±,μ±ℓ=e±,μ±, after typical acceptance and efficiency cuts, one expects about 90 and 300 top-quarks per nominal LHC-year and 4.7⋅1044.7⋅104 and 105 per FCC-year in Pb–Pb and p–Pb collisions respectively. The total tt¯ cross sections, dominated by gluon fusion processes, are enhanced by 3–8% in nuclear compared to p–p collisions due to an overall net gluon antishadowing, although different regions of their differential distributions are depleted due to shadowing or EMC-effect corrections. The rapidity distributions of the decay leptons in tt¯ processes can be used to reduce the uncertainty on the Pb gluon density at high virtualities by up to 30% at the LHC (full heavy-ion programme), and by 70% per FCC-year. The cross sections for single-top production in electroweak processes are also computed, yielding about a factor of 30 smaller number of measurable top-quarks after cuts, per system and per year.