Search for an A boson decaying to Zh, within the fully hadronic ℓℓィィ final state, in pp collision data recorded at √s = 8 TeV with the ATLAS experiment

Abstract

A search for the pseudoscalar A boson, which is predicted by in many models with an extended Higgs sector, gives a gateway to searches for physics beyond the Standard Model (SM). This thesis presents the results of a search for gluon-fusion produced A in the decay to Zh, with a final state of two electrons or muons and two τ leptons, in 20.3 fb−1of proton-proton collision data at √s = 8 TeV. Each tau lepton is allowed to dacay either leptonically, τlep, or hadronically,τhad, giving rise to three final states, τlepτlep, τlepτhad and τhadτhad. Focus is placed on the methodology and results of the fully hadronic channel. No evidence for the existence of an A boson is found in the scanned range of 220 ≤ mA ≤ 1000 GeV and 95% CL upper limits are placed on the gluon-fusion cross section times branching ratio, σ × BR(A → Zh) × BR(h → ℓℓττ). The results are combined with a complementing A → Zh search, where h → b¯b, and interpreted in view of two-Higgs-Doublet-Models (2HDMs), where exclusion limits are placed on large sections of phasepace.