Search for new Physics in Boosted hh $\to$ bb$\tau \tau$ Decays

The resonant and non-resonant production of two Higgs bosons play an important role in the investigation of the Higgs self-coupling and in searches for physics beyond the Standard Model. Due to the relatively high Higgs mass and its narrow width, decays into two Higgs bosons are ideal e.g. in searches for heavy Higgs bosons or heavy Kaluza-Klein gravitons. Furthermore the hh $\to$ bb$\tau \tau$ decay channel is promising as the Higgs decay into a pair of b quarks has the highest branching ratio, while the decay into $\tau \tau$ final states has still a moderately high branching ratio and allows good separation against QCD background. In particular the regime of very high mass resonances above 1 TeV is experimentally challenging. The high boost of the two b quarks and the two $\tau$ leptons lead to signatures with close-by pairs of b jets and $\tau$ decays in the ATLAS detector and requires dedicated experimental techniques to tag those topologies. This talk presents how the search for new physics in the bb$\tau \tau$ final state can be extended to the regime of high mass resonances above 1 TeV. For that purpose the latest developments in the identification of highly boosted $\tau$ pairs in the fully hadronic decay channel are presented. It will be shown how these new techniques apply to the bb$\tau \tau$ final state and how the main background coming from multi-jet events can be estimated. The reconstruction and identification of boosted $\tau$ pairs is furthermore verified in boosted Z boson decays.