Master thesis defence by Daniel Stefaniak Nielsen – University of Copenhagen

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Master thesis defence by Daniel Stefaniak Nielsen

Detector optimization and/or searches for new physics with ATLAS

Abstract: The Large Hadron Collider has increased the center-of-mass energy to 13 TeV for Run 2. The higher energy has allowed analyses to search for new and ever-heavier particles. This thesis will present a series of attempts at improving the diboson analyses in the boosted regime.
A small study into improving the charge calculation of jets is presented. The current equation for jet charges will be extended to include a new weight, and the parameter dependence on the transverse momentum of the jets will be included. This gives an improved charge separation between W bosons.
The main study will look into using machine learning to improve signal significance. The analysis will focus on the semi-leptonic channel of an HVT particle decaying to two W bosons. Instead of cutting on the classifier scores, they will be used in a simultaneous likelihood fit with W and signal masses. The study shows the stepwise improvement of including more variables in the simultaneous fit.