Reconstruction of challenging signatures characteristic to new physics beyond the Standard Model

Sammanfattning: A study of photon-jets and their identification variables computed in the electromagnetic calorimeter of an in-house, ATLAS-like, detector model developed at Uppsala University for full-simulations is presented. The signal, which is based on the Composite Higgs Model, considers the pair production of vector-like top quarks, denoted t', with the successive decays t' to S and a Standard Model top quark and S to two photons, where S is a new pseudo-scalar boson. For clustering purposes, Topological Clustering was implemented and compared against the already implemented Sliding Window clustering algorithm. A modification to the Topological Clustering algorithm used in the ATLAS detector was made and compared against the original version. The performance test showed a significant mass reconstruction improvement with Topological Clustering. Furthermore, the performance test showed some improvement with the modifications in the Topological Clustering for photons in a collimated scenario. The signal is compared to Standard Model background consisting of one photon plus zero, one or two jets, and isolated photons from the Higgs boson decaying into two photons. Even though some discrimination could be found, the analysis showed that standard cut and count strategy won't work and hence, further analysis with machine learning should be tested.