A Search for Physics Beyond the Standard Model using Like-Sign Muon Pairs in $pp$ Collisions at $\sqrt{s} = 7$ TeV with the ATLAS Detector

This dissertation presents a search for physics beyond the Standard Model using pairs of muons with equal electric charge. The search is performed in a proton-proton collision data sample collected during 2011 at $\sqrt{s} = 7$ TeV by the ATLAS experiment at the Large Hadron Collider. The total data sample corresponds to an integrated luminosity of 4.7 fb$^{-1}$. Events are selected by requiring pairs of prompt and isolated like-sign muons with transverse momentum greater than 20 GeV. The observed dimuon invariant mass distribution is compared to the Standard Model expectation, searching for any deviation between the observed and predicted yields. No evidence for an excess beyond the Standard Model expectation is observed. The results are interpreted as inclusive cross-section limits on the production of like-sign muon pairs from non-Standard Model sources as function of the dimuon invariant mass. The cross-section limits range between 30 fb and 1.2 fb. The data are also searched for a new narrow resonance which decays to like-sign muon pairs. No evidence for such resonant production is observed and the results are interpreted as upper limits on the mass and production cross section of doubly charged Higgs bosons. Assuming pair-production and a 100% branching ratio to muons, masses below 398 GeV (306 GeV) are excluded assuming coupling to left-handed (right-handed) fermions.