The ATLAS (A Toroidal LHC Apparatus) experiment, worldwide collaboration of more than 3000 scientists from 175 institutions in 38 countries, is conducting researches at the Large Hadron Collider (LHC), worlds largest hadron collider.Designed to collide proton beams at a 14 TeV center of mass energy and a 1034 cm-2s-1 peak luminosity, the LHC ran at 7 TeV in 2011 and 8 TeV in 2012, this running period is referred to as Run 1.Shut down during 2013 and 2014 for an upgrade, the LHC was restarted in 2015 at 13 TeV.The general purpose ATLAS detector, provides a rich physics potential for precise measurements of the Standard Model (SM) and search for new physics phenomena.The ATLAS experiment is a.Two physics analyses, to which I have strongly contributed,are presented in this thesis document.The first one is the search for W±W±W(±) and the study of anomalous quartic gauge couplings (aQGC).This is a search for the tri-boson W±W±W(±) production decaying in full leptonic channel and semi leptonic channel, my contribution is in the full leptonic channel.This analysis utilizes Run 1 data collected at 8 TeV and 20.3 fb-1 integrated luminosity.In the full leptonic channel, backgrounds can come from WZ and ZZ processes with three real leptons, this background is estimated with the Monte Carlo simulation.Events with mis-reconstructed leptons or charge mis-identified leptons are important background contributions as well, referred as reducible background and estimated with data-driven methods.The measurement of aQGC provides a sensitive probe for new physics beyond the Standard Model (SM) at high energy scale.The WWWW vertex is used to conduct the aQGC study.The number of events observed is consistent with the SM prediction.The observed upper limit at 95％ CL on the SM W±W±W(±) cross section is 730 fb with an expected limit of 560 fb in the absence of the W±W±W(±) production.Since no significant deviation from the SM is observed, limits on anomalous quartic gauge couplings are also derived.The second physics analysis I joined, is a search for doubly charged Higgs performed on Run 2 data collected in 2015 and 2016 at 13 TeV with a 36.1fb-1 integrated lu minosity.The doubly charged Higgs is predicted by a model that extends the SM to allow masses for neutrinos.In this model, also called Higgs Doublet Triplet Model, a triplet scalar is introduced in the Higgs sector and the electroweak symmetry breaking introduces several Higgs bosons, one of them with a doubly charged, the H±±.Various constraints are applied to simplify the scenario and only the pair-produced H±± mode where all H±± decays to W bosons is considered in the analysis for a mass range from 200 to 700 GeV.There are three channels, named according to the different final states,in this analysis: 2lss, 3l and 4l.I worked in the 2lss channel where background is more complex to deal with.The backgrounds can come from events with two same sign leptons such as the W±W± process, this background is estimated with MC simulation.Events with charge mis-identified leptons or with mis-reconstructed leptons are important background contributions which are estimated with data-driven methods and their correlations are properly dealt with.In this analysis, background is found to be consistent with the data and no significant excess observed.Therefore, upper limits are derived and the model is excluded at 95％ CL for MH±± ＜ 220 GeV.