Evidence for the Higgs Boson Decay to t⁺t^- in the Lepton + Hadrons Final State with ATLAS

Abstract

The data recorded with the ATLAS experiment during the first run period of the Large Hadron Collider are analysed by selecting final states with two τ-leptons, which further decay to a lighter lepton and to hadrons, respectively. The modelling of these final states is first validated in the context of the Z boson production cross section in ττ final states. The event selection and the data-driven techniques for the estimation of important background processes are then adapted to a search for H→ττ decays of the Higgs boson. In this search, Z→ττ final states contribute the dominant background and are therefore modelled in a data-driven way by replacing the Z decay products in Z→μμ data events with simulated decays of τ-leptons. Including all different background estimates, the search strategy is developed, and its sensitivity is documented in two intermediate results. With the final multi-variate analysis employing boosted decision trees, an excess of data over the estimated background in lepton + hadrons final states is observed with a statistical significance of 3.2$sigma$. It is compatible with a mass of m_Happrox125 GeV, which has been measured in other final states originating from bosonic decays. This result is evidence for the Yukawa coupling of the Higgs boson to μ-leptons.