María Aldaya Martín

A bstract A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data sample corresponds to an integrated luminosity of 138 fb − 1 of proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.

We study the impact of the top quark mass renormalized in the $\overline{\text{MS}}$ scheme on the $\text{t}\bar{\text{t}}\text{H}$ production cross-sections as an alternative to theory predictions with the conventionally used pole mass scheme. The differential cross-sections at next-to-leading order in perturbative QCD with stable top quarks show a moderate decrease in scale uncertainties for the $\overline{\text{MS}}$ mass renormalization scheme compared to the on-shell one. The shape of the differential distributions is not affected much, the largest differences being observed in the invariant mass distributions of the $\text{t}\bar{\text{t}}$ and the $\text{t}\bar{\text{t}}\text{H}$ systems.

Tesis Univ. Granada. Departamento de Fisica Teorica y del Cosmos. Leida el 11 de julio de 2008

We study the impact of the top quark mass renormalized in the $\overline{\text{MS}}$ scheme on the $\text{t}\bar{\text{t}}\text{H}$ production cross-sections as an alternative to theory predictions with the conventionally used pole mass scheme. The differential cross-sections at next-to-leading order in perturbative QCD with stable top quarks show a moderate decrease in scale uncertainties for the $\overline{\text{MS}}$ mass renormalization scheme compared to the on-shell one. The shape of the differential distributions is not affected much, the largest differences being observed in the invariant mass distributions of the $\text{t}\bar{\text{t}}$ and the $\text{t}\bar{\text{t}}\text{H}$ systems.

We study the impact of the top quark mass renormalized in the $\overline{\text{MS}}$ scheme on the $\text{t}\bar{\text{t}}\text{H}$ production cross-sections as an alternative to theory predictions with the conventionally used pole mass scheme. The differential cross-sections at next-to-leading order in perturbative QCD with stable top quarks show a moderate decrease in scale uncertainties for the $\overline{\text{MS}}$ mass renormalization scheme compared to the on-shell one. The shape of the differential distributions is not affected much, the largest differences being observed in the invariant mass distributions of the $\text{t}\bar{\text{t}}$ and the $\text{t}\bar{\text{t}}\text{H}$ systems.