B2b: Operator Analysis of New Physics in Top-Quark Observables

Principal Investigators
Jun.-Prof. Susanne Westhoff Heidelberg University


Top-quark interactions can be tested to high precision directly in resonant top production at the LHC, as well as indirectly in flavor and electroweak precision observables. We perform a model-independent global search for physics beyond the Standard Model in top-quark ob- servables in the framework of an effective field theory (EFT), described by $${\cal L}_{\rm eff} = \sum \limits_{i} \frac{C_i}{\Lambda^2} {\cal O}_i + {\cal O}(\Lambda^{-3}).$$ In this framework, effects of new physics in different observables are correlated in a predic- tive way. For example, the effective operator $${\cal O}_{tW} = \left (\bar Q_L \sigma^{\mu \nu} \tau^\alpha t_R \right ) \tilde H W_{\mu \nu}^{\alpha}$$ contributes to electroweak single top production at the LHC, but also to rare meson decays.

In our global analysis, we connect top-quark and Higgs observables with flavor observa- bles by matching the EFT {Ci Oi} from Eq. (1) onto the weak effective theory {Ci Oi} and evolving the Wilson coefficients down to the energy scale of meson decays.

The EFT connection between flavor and high-energy observables depends on the flavor struc- ture of the Wilson coefficients Ci at high energies. We identify new search directions in high- energy processes that are compatible with a specific flavor structure and thus guide future searches for new physics with top-quarks.


  1. Precise predictions of new physics effects in top-quark observables
    • Computation of top-quark LHC observables in the effective theory at NLO QCD.
    • Monte-Carlo simulations of cross sections and kinematic distributions.
  2. Global data analysis and interpretation
    • Global fit of top observables to LHC data, using analysis tool SFitter. ◦ Detailed analysis of systematic uncertainties and correlations.
    • Interpretation of fit results in terms of Wilson coefficients.
  3. Combination of high- and low-energy observables
    • Include flavor observables with virtual top-quarks in global analysis.
    • Connect observables at different energy scales through renormalization group evolution at LO QCD.
    • Impact of flavor observables on flavor structures of Wilson coefficients.
  4. Future goals
    • Include Higgs and electroweak observables in global fit.
    • Investigate effects of CP violation in top-quark interactions.
    • Interpret fit results in terms of complete models of new physics.
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