Reconstruction and Identification of Boosted Tau Pair Topologies at ATLAS

Decays that involve a pair of tau leptons in the final state are important channels for the search of heavy resonances, which are predicted by theories that go beyond the Standard Model of particle physics. With the restart of LHC in 2015 higher energies and particle masses will be reachable for these processes. Thus, in particular the understanding of highly boosted tau pairs in the high energy region is essential for the search for new physics. With the current approach of tau reconstruction it is not possible to reconstruct di-tau topologies with low spatial separation. % two tau leptons with a low distance separately. Due to the usage of anti-$k_t$-4 seed jets, tau leptons with a sum of transverse momenta of $p_\mathrm{T} \gtrsim 500\,\mathrm{GeV}$ or respectively an angular distance of $\Delta R < 0.4$, merge into the same jet. Therefore, in this thesis a new approach of di-tau reconstruction is introduced, which extends the sensitivity to tau pair decays to up to $p_\mathrm{T} \approx 1200\,\mathrm{GeV}$ by reconstructing a di-tau topology in one anti-$k_t$-10 seed jet. Additionally, with the di-tau identification a multi-variate background separation algorithm is developed, which is able to discriminate QCD di-jets with a high efficiency.