Search for scalar bottom quarks in compressed final states with b-jets and missing transverse momentum with the ATLAS detector

A search for the direct production of bottom squark pairs according to R-parity conserving supersymmetric models is presented in this thesis. The search targets final states with b-jets and missing transverse momentum. The analysis is based on 139 fb-1 of proton-proton data collected by the ATLAS detector at the LHC at a centre-of-mass energy ps = 13 TeV. Simplified models where the bottom squark decays into a bottom quark and the lightest, stable neutralino are targeted, and scenarios where the two supersymmetric particles are almost mass-degenerate are considered by this analysis. The compressed final states originating from these simplified models are reconstructed by exploiting a novel secondary-vertex identification technique to detect low momentum b-hadrons using tracks from the ATLAS inner detector. The performance and calibration of this algorithm are presented in this thesis. The analysis shows no significant deviations from Standard Model predictions and stringent exclusion limits are placed on the bottom squark masses for the examined simplified model. Bottom squark masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV are excluded at 95 % CL.