Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at $\sqrt{s} = $ 13 TeV

TL;DR

This study searches for new top quark interactions via effective field theory in top-Z associated production at 13 TeV, using CMS data and machine learning to set limits on possible new physics effects.

Contribution

It introduces a comprehensive analysis of five dimension-six operators affecting top-Z interactions using multilepton final states and advanced machine learning techniques.

Findings

No significant deviation from the Standard Model observed.

95% confidence level limits set on Wilson coefficients.

Enhanced sensitivity achieved through novel machine learning methods.

Abstract

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 $\sqrt{s} =$ 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.