Search for new heavy, charged gauge bosons with the ATLAS detector

The subject of this thesis is the search for new charged bosons beyond the predictions of the Standard Model. The existence of new heavy charged vector bosons is investigated in events containing a muon and neutrino pair. Neutrinos are observed indirectly via the presence of high missing transverse energy. We analyze data from proton-proton collisions at center of mass energy of 8 TeV, collected by the ATLAS detector during the operation of the Large Hadron Collider in the years 2011-2012, corresponding to an overall luminosity of20.3 fb-1.Two main new-physics scenarios are investigated: The first new-physics scenario that is considered in this thesis is the Sequential Standard Model (SSM). This model proposes the existence of additional heavy gauge bosons, of which the charged ones are commonly denoted as W′. The W′ has the same couplings to fermions as the Standard Model W boson and a width that increases linearly with the W′ mass.The second new-physics scenario that is considered proposes the existence of charged partners, denotedW*, an excited state of the Standard Model W boson. The anomalous (magnetic-moment type) coupling of the W* leads to kinematic distributions significantly different from those of the W′.Α strict data event selection is applied in order to reduce the background, which comes mainly from W boson decays. All background sources were simulated, except the multijet background, which was estimated from the experimental data. Finally, all sources of systematic uncertainty are carefully evaluated.The analysis of data showed that the number of events observed is consistent with the number of background events expected, so there is no evidence for the existence of new, heavy charged gauge bosons. Therefore, limits are set to the σ * B (cross-section * branching ratio) for W 'and W * in the mass range of 0.5 - 4 TeV.In the analysis presented in this thesis, the limits are considerably improved in the region covered by the previous search.