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dc.contributor.authorLewis, Dave
dc.identifier.citationLewis, D. 2017. New Physics at the LHC: Direct and Indirect Probes. Queen Mary University of Londonen_US
dc.description.abstractThis thesis presents the results for two searches for new physics performed with the ATLAS experiment. The first, a search for the rare B-meson decay Bs ! and measurement of its branching ratio, uses 25 fb1 of ps = 7 and 8 TeV data recorded during 2011 and 2012. After observing a small number of these decays, a branching ratio of B(Bs ! ) = (0:9+1:1 ��0:8) 10��9 is measured, assuming non-negative event yields. This is compatible with the Standard Model at the 2 level. The second, a search for direct pair production of the supersymmetric top quark partner, is performed using 36.07 fb��1 of p s = 13 TeV data recorded during 2015 and 2016. Final states with a high jet multiplicity, no leptons and large missing transverse momentum are selected to target these decays, with several signal regions designed to cover a wide range of particle masses. No excess is observed, with all signal regions being compatible with the Standard Model within 2 . Limits are set on the stop mass, excluding up to m~t1 = 940 GeV for values of m~ 01 below 160 GeV, assuming a 100% branching fraction to ~t1 ! t~ 01 decays. In addition two reinterpretations of this data are presented, for a gluino-mediated stop production scenario and a direct dark matter production scenario. No excess is observed for either model, and limits are set on the mass of the relevant particles. Finally a viability study into using machine learning techniques to improve on existing SUSY search methods has been performed, with the initial results proving promising.en_US
dc.description.sponsorshipScience and Technology Facilities Councilen_US
dc.publisherQueen Mary University of Londonen_US
dc.rightsThe copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the author
dc.subjectLarge Hadron Collideren_US
dc.subjectCERN ATLASen_US
dc.titleNew Physics at the LHC: Direct and Indirect Probesen_US

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  • Theses [2761]
    Theses Awarded by Queen Mary University of London

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