Searching for Supersymmetry in Boosted Fully-Hadronic Final States with B-Jets and Calibrating B-Jet Identification Using Spatially Matched Muons at the Atlas Detector
This thesis presents two analyses that involve the identification of hadronic jets produced by the fragmentation of b-quarks or "b-jets''. The identification exploits the hard fragmentation of b-quarks and relatively long lifetime of B hadrons. The first analysis is the calibration of the efficiency of the MV2c10 b-jet identification algorithm using a sample of b-jets with muons from B hadron decays and a kinematic property of these jets knows as "pTrel'', which is constructed from the muons. This analysis was performed using 68 fb-1 of data collected at √s = 13$ TeV with the ATLAS detector during Run 2 of the Large Hadron Collider. Improvements in the methods of this calibration have led to a reduction by more than an order of magnitude in the uncertainty of earlier measurements of b-jet tagging efficiency using this approach. This work included substantial contributions to the software and computing framework used to the study the identification of jets produced by heavy flavor decay; these contributions are described herein. The second analysis is a search for electroweakly-produced supersymmetric partners of the gauge bosons or "gauginos''. This search uses 140 \ifb\ of data collected at √s = 13 TeV with the ATLAS detector during Run 2 of the Large Hadron Collider. My work focused on developing a new signal region that targeted final states specifically containing two b-jets and two light-quark jets. As part of this optimization, I examined different supersymmetric scenarios and explored alternative techniques for estimating the Standard Model backgrounds. Based on preliminary results, in the wino-bino scenario, this search is expected to provide sensivity to charginos with masses up to ~1 TeV. For a scenario in the general-gauge-mediation model (where higgsino becomes the next-lightest SUSY particle), this search will provide sensitivity for higgsinos with masses up to 600 GeV (discovery) or 800 GeV (exclusion) for most of the possible Z/h branching ratios. Finally, the sensitivity to the scenarios where higgsino is next-lightest and bino is the lightest SUSY particle has been studied, on which no explicit exclusion has been reported yet by the searches in LHC.
Creager, Rachael Ann, "Searching for Supersymmetry in Boosted Fully-Hadronic Final States with B-Jets and Calibrating B-Jet Identification Using Spatially Matched Muons at the Atlas Detector" (2020). Dissertations available from ProQuest. AAI27744454.