Search For Resonances In The Dijet Mass Spectrum With The ATLAS Experiment At The LHC

The unprecedented collision energy reached and the considerable integrated luminosity produced by the LHC allow its experiments to investigate the existence of new physics phenomena beyond the Standard Model of particle physics at the TeV scale. This thesis presents the search performed by the ATLAS Collaboration for evidence of new physics manifesting as localised resonances in the dijet invariant mass distribution of events with large transverse momenta. No evidence of resonant phenomena outside of the Standard Model have been observed in the 20.3 fb$^{-1}$ of data collected in 2012 at $\sqrt{s}$ = 8 TeV nor in the 3.6 fb$^{-1}$ of data collected in 2015 at $\sqrt{s}$ = 13 TeV. Limits have been set at 95% Credibility Level on the cross-section times acceptance of selected benchmark models. Excited quarks with masses below 4.06 TeV and Quantum Black Holes, QBH, with masses below 5.2 TeV have been excluded using the 2012 datasets. These limits have then been further extended to 5.66 TeV (excited quarks) and 8.3 TeV (QBH) using the 2015 datasets. The reach of the dijet analysis at large integrated luminosities and at a collision energy of $\sqrt{s}$ = 14 TeV has been investigated. The analysis sensitivity to excited quarks and QBHs for $5\sigma$ discoveries is expected to improve by roughly 1 TeV for each additional order of magnitude of integrated luminosity and up to the 3000 fb$^{-1}$ to be delivered by HL-LHC, pushing the analysis reach to 6 TeV and 9-10 TeV for the two above-mentioned models by the end of Run-2.