The first measurement of the spin correlation strength in pairs of top quarks at √s=8 TeV is presented, using data collected using the ATLAS detector, corresponding to an integrated luminosity of 20.3 fb⁻¹. Dileptonically decaying tt^- events are selected with two high-pT leptons and at least two jets, one of which is required to be b-tagged. The azimuthal angle between the two charged leptons, Δφ, is used to measure the degree of spin correlation of top quark pairs. The extracted value of fSM, which is a measure of the spin-correlation strength, is fSM=1.20 ± 0.14. This is the most precise spin-correlation measurement to date. Using the Δφ distribution, a search for Supersymmetric top squarks is performed, with the assumption that the top squarks decay to a top quark and a neutralino. No excess of events is observed and top squarks with masses between the top quark mass and 191 GeV are excluded at 95% confidence level, extending previous limits.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:632326 |
| Date | January 2015 |
| Creators | Neep, Thomas James |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/a-measurement-of-spin-correlation-in-top-antitop-pairs-and-a-search-for-top-squarks-at-sqrts8-tev-using-the-atlas-detector(cfb7f020-f0b5-4040-a17c-cde6dcc8d08d).html |
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