Searches for Low-Mass Dijet Resonances in Trijet Final States using Monte Carlo Samples

Abstract: This thesis presents the prototype of a search for new phenomena that decay in two jets, in presence of an associated jet (three-jet or trijet final state). Mass combination studies are carried out to reconstruct dijet resonances in different mass regions. The two models of interest are the composite quark, which contains a composite quark resonance Q, and the simplified dark matter mediator model, which contains a dark matter mediator resonance Z'. Both models give rise to three-jet final states. The kinematic distributions for the two models are observed to be similar. The simplified dark matter mediator model is chosen to perform a sensitivity study. The study determines the luminosity at which the search for Z' becomes sensitive to a given resonance mass point. The resonance masses m_{Z'} considered in the study are 300-700 GeV in steps of 100 GeV. The search targets low-mass resonances and employs the BumpHunter algorithm used at the ATLAS experiment. All studies in this thesis are done using Monte Carlo samples.