Searches for Dijet Resonances : Using √s = 13 TeV Proton–Proton Collision Data Recorded by the ATLAS Detector at the Large Hadron Collider This book addresses one of the most intriguing mysteries of our universe: the nature of dark matter. The results presented here mark a significant and substantial contribution to the search for new physics in particular for new particles that couple to dark matter. The first analysis presented is a search for heavy new particles that decay into pairs of hadronic jets (dijets). This pioneering analysis explores unprecedented dijet invariant masses reaching nearly 7 TeV and sets constraints on several important new physics models. The two subsequent analyses focus on the difficult low dijet mass region down to 200 GeV and employ a novel technique to efficiently gather low mass dijet events. The results of these analyses transcend the long standing constraints on dark matter mediator particles set by several existing experiments Theoretical Background The ATLAS Experiment Physics Object Reconstruction in ATLAS Dijet Invariant Mass Spectra Searching for Resonances Limit Setting Conclusion and Outlook