Search for high-mass dilepton resonances in association with $b$-jets at the ATLAS experiment

In this thesis, a search for a Z' boson produced in association with $b$-jets is presented. The analysis uses the data from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13TeV$ collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of $36.2fb^{-1}$. A preliminary expected limit on the Z' production cross section is set to compare the sensitivity of the analysis approach to the sensitivity of previous inclusive searches. Systematic uncertainties are not considered. The analysis is carried out separately in the electron channel and the muon channel. A preselection region is defined, and the most important background processes are validated in dedicated regions. For the electron channel, a data-driven estimation of the multijet background is obtained via the Matrix Method. The Monte Carlo samples of the signal process are studied, and two different approaches for defining a signal region are introduced. A preliminary limit on the Z' production cross section is set and compared to the limit obtained by previous inclusive analyses. The limit on the Z' mass obtained in this analysis is lower than the limit obtained by the inclusive analyses. Overall, the chosen analysis approach is found to be limited by low event statistics in the high dilepton invariant mass region. The expected limits on the production cross section are lower than the limits of the inclusive analysis, but the smaller production cross section results in a lower exclusion limit on the Z' mass as well.