Search of new resonances decaying into top quark pairs in the lepton+jet final state in proton-proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for resonances produced in 13 TeV proton-proton collisions and decaying into top-quark pairs is presented. In this study events where the top-quark decay produces a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay recorded with the ATLAS detector at the Large Hadron Collider (LHC) are considered. We investigate the observed invariant mass spectrum in a model-independent approach to seek for any significant deviation from the Standard Model (SM) background expectation. The Matrix Method was used to estimate the QCD multi-jet background, which has large statistical and systematic uncertainties when modelled using Monte Carlo techniques. We have performed general searches for new resonances for a specific benchmark models: $Z^{'}_{TC2}$ boson, Kaluza-Klein gluon and Kaluza-Klein graviton that decay into top-quark pairs. Taking into account all uncertainties, results are in line with SM expectations. A synopsis of the results followed by an explanation of key findings will be presented.