Searches for Diboson New Physics and the L1Calo Software Development with the ATLAS Detector

The Standard Model has been a successful theory in describing the behaviour of fundamental particles, but there are still problems remaining unsolved. New theoretical models are therefore proposed to answer those questions with either new interactions or new particles. This thesis is presenting the searches for new physics with diboson signatures in these two ways from LHC $\sqrt{s} = 13 \mathrm{TeV}$ collisions with the ATLAS detector with the data collected in 2015 and 2016 corresponding to an integrated luminosity of $36.1 fb^{−1}$. The searching strategy was performed with the Monte Carlo simulation for the SM background modelling and a data-driven method for the multijet background estimation. The final result was interpreted by a comparison between background modelling and data by a CLs method. For the resonance search, no new particle was discovered, and mass limits are therefore set on the new particles from models taken as the interpretation benchmarks. For the study on new interactions in the signatures of vector boson scattering, the first measurement of this process with the semileptonic decay was given with a significance of $2.7σ$ in reasonable agreement with the SM prediction Both the LHC and ATLAS detector are now going through the upgrades for operations in 2021 with the $\sqrt{s} = 14 \mathrm{TeV}$ collisions. The ATLAS hardware calorimeter trigger is part of the upgrade project for the implementation of three new object processors: eFex, jFex, and gFex. This thesis will also present the construction of simulation system along with the expected performance of proposed object reconstruction algorithms for this new infrastructure.