A Search For New Heavy Charged Gauge Bosons at ATLAS

In this thesis the results of a search for new charged heavy gauge bosons with ATLAS detector are presented. The search is mostly performed using data taken between March and October 2010 corresponding to an integrated luminosity of 36 pb-1. The existence of new charged heavy gauge bosons is predicted by many extensions of the Standard Model, and the search for such a boson in this thesis has been optimized using, as benchmark, the model in which W' has the same couplings to fermions as Standard Model W boson, with interactions with other gauge bosons excluded. In addition to W' , another model denoted W*, representing the charged partner to the chiral bosons, has been considered. The experimental signature consists of a high-momentum lepton (a muon or an electron) and high missing transverse energy in the event due to the neutrino that escapes detection. The transverse mass distribution is used as a discriminant for identifying W' and W* candidates. The data show no evidence of excess above SM expectations, and are used to set limits on W'(W*) production cross section multiplied by the lepton branching ratio (sigma x B) for several mass points in range 0.5 TeV-1.75 TeV. A W' with SM couplings is excluded for mass below 1.49 TeV at 95% CL, while the exclusion for W* with couplings set in accordance is 1.35 TeV. A preliminary results of search for W'->munu with 205 pb-1 of data are also presented, with mass limit increased Mw' > 1.70 TeV. The ATLAS sensitivity in search for W' is analyzed as a function of the center of mass energy at LHC and collected integrated luminosity. With the increase of the collision energy to 8 or 9 TeV which were considered as possible scenarios for 2012 run, increase of the signal sensitivity is expected to be 10-15% with respect to 7 TeV run for the same amount of data.