Study of New Physics Phenomena Decaying in Four-Jet Signatures with the ATLAS Detector

Sammanfattning: Particle Physics is well described by the Standard Model (SM). However, there are phenomena in the universe that the model does not describe. Supersymmetry, which predicts a partner particle for all fundamental particles, is an extension of the SM that provides solutions to problems the SM cannot solve. Finding the partner particles is crucial in order to confirm the theory about Supersymmetry. When searching for new low-mass partner particles though, the search is limited by large backgrounds producing similar signatures in the detector, since not all events can be recorded. By recording only necessary jet-information, events become much smaller than entire events, leading to the possibility to save more events. This strategy is called Trigger Level Analysis (TLA). In this project simulated samples of two top squarks of masses 80 GeV/c^2, decaying into two jets each, were analyzed in order to understand if a Trigger Level Analysis (TLA) could be performed in a four-jet signature. Two different TLA cuts were implemented and compared, where the first one only preserved events with a leading jet with a minimum p_T of 185 GeV/c and three additional jets with a minimum p_T of 85 GeV/c, and the second one preserved events with with a leading jet of a minimum p_T of 185 GeV/c and a subleading jet with a minimum p_T of 85 GeV/c. Analyzing their average mass distributions, a peak at m_Avg=m_t was found for both, however, the number of events conserved for the TLA cut with the requirements on only the two leading jets was much higher, leading to the conclusion that this option is preferable.