THESIS
2023
1 online resource (ix, 154 pages) : color illustrations
Abstract
Since the discovery of the Higgs boson at the Large Hadron Collider at CERN by the ATLAS
and CMS experiments, measurements of its properties have been carried out. These measurements
have yielded results in good agreement with the Standard Model expectation. Signs of
new physics have not been discovered in the properties of the Higgs boson. The precision of
these measurements is limited by the amount of data. Continuous measurements on the dataset
of increasing size would be able to constrain the properties with shrinking uncertainties. This
would enable experiments to detect potential deviations from the Standard Model more precisely
and indicate the direction of future new physics searches.
This study aims to search for the potential violation in simultaneous charge conjugation
and pa...[
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Since the discovery of the Higgs boson at the Large Hadron Collider at CERN by the ATLAS
and CMS experiments, measurements of its properties have been carried out. These measurements
have yielded results in good agreement with the Standard Model expectation. Signs of
new physics have not been discovered in the properties of the Higgs boson. The precision of
these measurements is limited by the amount of data. Continuous measurements on the dataset
of increasing size would be able to constrain the properties with shrinking uncertainties. This
would enable experiments to detect potential deviations from the Standard Model more precisely
and indicate the direction of future new physics searches.
This study aims to search for the potential violation in simultaneous charge conjugation
and parity inversion, known as CP violation, in the Higgs boson couplings with the 2015-2018
ATLAS data. Among different Higgs boson decay modes, the four-lepton decay mode through
Z bosons is a “clean” channel at the Large Hadron Collider, despite its moderate branching ratio.
Events in this channel are well-separated from heavy multi-jet backgrounds. The electrons and
muons in this final state are fully reconstructable with high reconstruction efficiency. These
features make it a suitable channel to study the bosonic couplings of the Higgs boson. In
addition, vector boson fusion, as the subleading Higgs boson production channel at the Large
Hadron Collider, produces jets that are sensitive to CP violation. Their information is used
together with the four-lepton decay information in this study to optimize sensitivity.
In this study, the potential CP violation in the Higgs boson coupling to Z bosons is searched
through the measurement of the CP-odd couplings beyond the Standard Model. The CP-odd
couplings measured are parametrized using the effective field theory framework. The measurement
is based on the likelihood fit method of the normalized kinematic observable distributions
of the leptons and jets in the final state.
The results of this study are consistent with the Standard Model expectation within two
standard deviations. The statistical fluctuations of data are the dominant source of uncertainties
in this analysis. More strict constraints than the previous yield-based analysis have been set
in the CP-odd effective couplings. This measurement inspires a deeper understanding of the
coupling structure of the Higgs boson.
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