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EFT results in the top quark sector in CMS

Andrea Piccinelli

TL;DR

CMS reports an SMEFT program in the top-quark sector combining CP-violation searches in ttZ and tZq, flavour-structure tests in multilepton final states, and Run 2 top+X combinations. Analyses fit dimension-6 operators in the Warsaw basis, using physics-informed observables to constrain CP-odd and flavour-dependent Wilson coefficients, such as c^I_{tW}, c^I_{tZ}, and flavour-split operators; the framework is encoded in the effective Lagrangian $L_eff = L_SM + sum_i (c_i / Lambda^2) O_i + ...$. HL-LHC projections indicate improvements by roughly a factor of 2–4 in indirect sensitivity. The work demonstrates the value of multi-process, ML-informed analyses for expanding indirect new-physics reach in the top sector.

Abstract

The CMS programme of indirect searches in the top-quark sector interprets precision measurements in the Standard Model Effective Field Theory (SMEFT) framework. These proceedings summarize recent CMS results highlighted in the TOP2025 talk: a search for CP violation in ttZ and tZq production using CP-odd observables constructed with physics-informed machine learning, a measurement that disentangles the flavour structure of electroweak SMEFT couplings in multilepton final states, and a Run 2 combination of complementary top+X measurements. We close with a brief outlook on the expected sensitivity gains at the high-luminosity LHC.

EFT results in the top quark sector in CMS

TL;DR

CMS reports an SMEFT program in the top-quark sector combining CP-violation searches in ttZ and tZq, flavour-structure tests in multilepton final states, and Run 2 top+X combinations. Analyses fit dimension-6 operators in the Warsaw basis, using physics-informed observables to constrain CP-odd and flavour-dependent Wilson coefficients, such as c^I_{tW}, c^I_{tZ}, and flavour-split operators; the framework is encoded in the effective Lagrangian . HL-LHC projections indicate improvements by roughly a factor of 2–4 in indirect sensitivity. The work demonstrates the value of multi-process, ML-informed analyses for expanding indirect new-physics reach in the top sector.

Abstract

The CMS programme of indirect searches in the top-quark sector interprets precision measurements in the Standard Model Effective Field Theory (SMEFT) framework. These proceedings summarize recent CMS results highlighted in the TOP2025 talk: a search for CP violation in ttZ and tZq production using CP-odd observables constructed with physics-informed machine learning, a measurement that disentangles the flavour structure of electroweak SMEFT couplings in multilepton final states, and a Run 2 combination of complementary top+X measurements. We close with a brief outlook on the expected sensitivity gains at the high-luminosity LHC.
Paper Structure (5 sections, 1 equation, 2 figures)

This paper contains 5 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. Search for CP violation in ttZ and tZq
  3. Flavour structure of electroweak SMEFT couplings in multilepton final states
  4. Combinations and projections
  5. Conclusions

Figures (2)

  • Figure 1: Likelihood scans in the $(c^{I}_{tW},\,c^{I}_{tZ})$ plane for the $CP$-violation search in $t\bar{t} Z$ and $tZq$ production. Left: linear EFT contributions only. Right: linear and quadratic contributions. The SM point is indicated by a cross. Adapted from CMS_CPViolation_ttZtZq_2025.
  • Figure 2: Summary of best-fit values and confidence intervals for selected WCs in the flavour-structure measurement in multilepton final states. Results are shown for scans with other coefficients fixed to zero and for profiled fits. Heavy-quark couplings are scaled by 0.1 for visibility. Adapted from CMS_FlavorStructure_EFT_Multilepton_2025.