Kunkle, Joshua Milo

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  • Publication
    A Search for Dark Matter Through Invisible Decays of the Higgs Boson With the Atlas Detector at the LHC
    (2013-01-01) Kunkle, Joshua Milo
    Diboson physics provides insight into a wide variety of processes that are produced copiously at the LHC. Of particular interest are events where leptons and neutrinos are produced, strong signatures of electroweak physics. The study of electroweak physics is essential to understanding the Standard Model and in searches for phenomena outside the Standard Model. The most sensitive channels that contributed to the discovery of the Higgs boson searched for decays to dibosons. This thesis will present four analyses that utilize charged leptons and neutrinos whose presence are inferred from the missing transverse momentum. Two measurements of Standard Model cross sections will be presented. The WW cross section is measured using 35 pb-1 of data collected in 2010 and is one of the earliest measurements of diboson processes at the LHC. The ZZ cross section is measured using 4.6 fb-1 of data collected in 2011. A search for the Higgs in the WW decay channel is presented also using 4.6 fb-1 of data collected in 2011. This analysis did not have the sensitivity to discover the Higgs boson, but when data were added in 2012 this channel contributed significantly to its discovery. Finally a search for anomalous invisible decays of the Higgs boson using 4.6 fb-1 of data taken in 2011 and 13.1 fb-1 of data taken in 2012 will be presented. This search is sensitive to new physics that couples to the Higgs boson that would result in an increased rate of decays to invisible particles. One possible scenario is that dark matter couples to the Higgs boson. If the mass of the dark matter particle is less than half of the mass of the Higgs boson decays to dark matter increase its invisible branching fraction. Dark matter is a significant contribution to the makeup of the universe, but very little is known about it. This search provides additional limits on how dark matter can couple to the Standard Model. No excess of events is observed in this search and limits are placed on the allowed invisible branching fraction. These limits are interpreted in the context of simple Higgs portal models to place constraints on the allowed dark matter mass and interaction cross section. The results are compared with current limits on dark matter and place significant restrictions on the allowed dark matter mass and cross section within these models.