Development of tools for Bayesian data analysis and their application in the search for physics beyond the Standard Model
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Date
2021
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Abstract
In this thesis, methods for Bayesian data analysis are employed in the search for physics beyond the Standard Model (BSM). A new implementation of the Bayesian Analysis Toolkit in
Julia (BAT.jl) is introduced as a modern data analysis framework providing algorithms for
Bayesian inference. The EFTfitter.jl package for interpreting measurements in the context of
effective field theories (EFTs) is presented. It facilitates combining measurements and estimating underlying parameters with Bayesian inference. Both tools are employed for indirect
BSM searches using EFTs. Wilson coefficients of dimension-six operators from the top-quark
sector of the Standard Model effective field theory (SMEFT) are constrained, and approaches
for enhancing fits of SMEFT coefficients are investigated. Studies on the effects of correlations
between the uncertainties of measurements on the results of SMEFT fits are conducted. It is
demonstrated that the correlations can significantly impact the resulting constraints and can
be the crucial components deciding whether deviations from the Standard Model of particle
physics are observed or not, in particular when assuming future measurements with reduced
uncertainties. Moreover, studies on combining measurements of top-quark and flavor physics
observables for SMEFT interpretations are performed, and the steps necessary for a combined
fit are discussed. Powerful synergies between top-quark processes and b → s transitions are
observed when constraining SMEFT Wilson coefficients of the top-quark sector. It is demonstrated that due to complementary sensitivities, combining observables from different energy
scales can tighten the constraints significantly. Future scenarios assuming measurements from
HL-LHC, Belle II, and CLIC are investigated, and their potential for improving constraints
on up to eleven SMEFT Wilson coefficients is pointed out. The benefits of orthogonal constraints in multidimensional phase spaces for resolving ambiguous solutions are highlighted.
The SMEFT studies presented in this thesis demonstrate the capabilities of the new BAT.jl
and EFTfitter.jl packages for BSM analyses.
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Keywords
Bayesian data analysis, Bayesian analysis toolkit (BAT), Physics beyond the Standard Model, SMEFT, EFTfitter, Top-quark physics, Flavor physics, Effective field theory