Searches for Heavy Charged Long-Lived Particles with the ATLAS Detector

In this thesis a search for Heavy Charged Long-Lived Particles (HCLLPs) in a dataset of 36.1/fb of proton–proton collisions with the ATLAS detector at the Large Hadron Collider is presented. HCLLPs manifest in the detector by signatures of heavy muon-like particles and are expected to be produced with velocities, significantly lower than the speed of light. Accordingly they are also expected to have an ionisation energy loss larger than that of muons, which are the main background for this search. Beside their electrical charge, HCLLPs can also be colour charged and hadronise together with Standard Model quarks to so called $R$-hadrons. Those $R$-hadrons can have a very special signature as they are able to change their overall charge through the exchange of the Standard Model quarks in hadronic interactions. The observables used to identify HCLLPs in this analysis are a d$E$/d$x$ estimate with the pixel detector and time-of-flight measurements with the Tile Calorimeter, the Monitored Drift Tubes and the Resistive Plate Chambers. The signal regions are designed to cover signatures of colour-charged particles that can undergo a change of charge as well as pair-produced colour singlets that are charged throughout the whole detector. No significant excess over the estimated background was observed and the results are used to set upper limits on the production cross section as well as lower mass limits for several models. The obtained lower mass limits for sbottom, stop and gluino $R$-hadrons are 1250 GeV, 1340 GeV and 2000 GeV, respectively, while for colour singlets such as staus and charginos 430 GeV and 1090 GeV are obtained.