Probing initial state effects in nuclear collisions via jet and top quark measurements with the ATLAS detector

Proton-lead collisions at LHC energies offer a unique possibility to investigate initial state effects in nuclear collisions. Thanks to its wide acceptance, ATLAS can measure several probes that can help characterize these effects over a wide kinematic range. By analyzing the centrality dependence of dijet production, it is possible to investigate the suppression of dijet events in central events compared to peripheral ones and correlate it to the kinematic of the parton-parton scattering, accessible thanks to the measurement of both jets in the final state. In 2016, the ATLAS experiment collected 165~nb$^{-1}$ of proton-lead collisions at a centre-of-mass energy of 8.16 TeV per nucleon pair. In this talk, we will present a new measurement of the centrality dependence of dijet production obtained using this dataset. We will also present the first measurement of the inclusive cross-section for top-quark pair production in dilepton and lepton+jet decay modes. This process is sensitive to effects at high Bjorken-x values, which are hard to access experimentally using other available probes, and thus provides complementary information on the behavior of nuclear parton densities.