Lubatti, Henry JBlackburn, Daniel Ryan2016-03-112016-03-112016-03-112015-12Blackburn_washington_0250E_15360.pdfhttp://hdl.handle.net/1773/35298Thesis (Ph.D.)--University of Washington, 2015-12A search is presented for the decay of the Standard Model Higgs boson or another scalar boson to a pair of weakly-interacting, long-lived particles in 20.3 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 8$ TeV recorded in 2012 by the ATLAS detector. The strategy requires that one of the long-lived particles decay inside the muon spectrometer. The second long-lived particle is required to decay in the inner detector or the muon spectrometer. No excess of events is observed above the expected background. Limits are derived on the scalar boson's production cross section times branching ratio as a function of the long-lived particle's proper decay length.application/pdfen-USPhysicsParticle physicsphysicsThesis