Search for long lived massive particles with the ATLAS detector at the LHC

In this thesis I have developed a method for extracting dE/dx estimates from the ATLAS calorimeters. I have shown that the dE/dx measurements of R-Hadrons from the calorimeters are similar to those of slow moving Standard Model particles in less dense detectors, clearly discriminating them from Standard Model particles, as they would either be stopped or minimum ionising in the same environment. This method have potential applications in further searches for penetrating charged particles at other experiments. I have developed a mass estimation method based on dE/dx measurements. The mass estimation calibration can in principle be used to calibrate to other functions than the one used in this analysis, as it simply provides a robust 2D fitting method. I have applied the mass estimation method to collision data, showing recognisable mass peaks for low momentum kaons, protons and deuterons. The calorimeter dE/dx estimators and the mass estimates have been used in a search for stable gluinos, hadronising into R-Hadrons. The search have placed an upper limit on gluino production at √s = 7 TeV with 15.3 pb−1 data. In comparison with the Split-SUSY scenario the limit corresponds to an exclusion of stable gluinos with masses less than 450 GeV.