Beyond Standard Model Higgs boson searches at a High-Luminosity LHC with ATLAS

The ATLAS experiment at the LHC is in an excellent position to study possible extensions of the Higgs sector of the Standard Model. This note reports results on the expected sensitivity to some beyond-the-Standard-Model physics scenarios with 300 and 3000 fb$^{−1}$ of pp data at $\sqrt{s}$ = 14 TeV. Three benchmark processes are studied here. The scenario of a gluon-fusion produced narrow CP-odd particle, A, which decays to Zh, where h is the Standard-Model- like Higgs boson discovered at the LHC, is motivated by two-Higgs-doublet models. The discovery potential for heavy Higgs bosons decaying to a di-muon pair is also explored. Finally, the projected sensitivity to heavy Higgs boson decays H -> ZZ -> lll′l′, where l,l′ = e or μ, and with mH in the range 0.2 – 1 TeV, is presented.