Gray, Chloe
(2019)
Kinematic properties of b-quark pairs in boosted Z+bb events and the search for V(H ->bb).
PhD thesis, University of Glasgow.
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Abstract
The study of b-quarks is very important as they play an important role in many Higgs and beyond the-Standard-Model searches, and their treatment using perturbative quantum chromodynamics (QCD) is not completely understood. This thesis presents a measurement of cross-sections for the production of a boosted Z-boson in association with a large-radius jet, differential in kinematic variables of the jet and its b-tagged sub-jets. This measurement provides an important test of perturbative QCD with emphasis on the production rates and kinematics of the bottom quarks. The phase space probed in the measurement is particularly relevant for beyond-the-Standard-Model searches. The differential and total cross-sections are presented at particle-level, where the fully Bayesian unfolding method was used to correct the data. The Z + bb̄ process is a significant background to several important Higgs-boson searches; a particular example being the search for a Higgs boson decaying to b-quarks, produced in association with a vector boson, V (H →bb̄). A study of the signal-modelling uncertainties in the 2017 search for V (H →bb̄), where the first evidence for the H → bb̄ decay was observed, is presented in this thesis. These analyses would not be possible without b-tagging algorithms to identify the b-quarks in the final state. It is important that the performance of b-tagging algorithms in data is well modelled by Monte Carlo simulation. A calibration of the b-tagging efficiency of the MV2c10 algorithm in small-radius track-jets is therefore also presented.
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