School of Physics - Theses
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ItemThe search for the Higgs boson in tauon pairs at the ATLAS experiment( 2013)The Higgs boson is a particle that’s predicted to exist by spontaneous electroweak symmetry breaking. Electroweak symmetry breaking is an essential part of the Standard Model of particle physics, as it generates masses for the electroweak gauge bosons. Finding the Higgs boson is integral to our understandings of the fundamental particles and their interactions. Searches for the Higgs boson are conducted by the ATLAS experiment using proton-proton collisions at the Large Hadron Collider. One of these searches is performed using the H→ττ decays, which has a clean detection signature and, with H →bb, is one of the only two viable fermonic search channels. Using the 4.7 f b−1 of data collected at √s = 7 TeV, the H→ττ analysis excludes the Higgs boson at approximately 3 times the expected cross section for 100 < mH < 120 GeV and 5 to 12 times the expected cross section for 130 < mH < 150 GeV. The H→ττ search results are combined with those from the other channels to achieve better sensitivities. The combined results have excluded most Higgs masses between 110 and 500 GeV. The only region that is not excluded is at mH = 126 GeV, where an excess above the background expectations is observed in multiple bosonic channels. This excess has a combined local significance of 5.9 σ. ATLAS claims this observed excess as a discovery of a new bosonic particle, whose properties have thus far been measured to be consistent with that of the Higgs boson.