An analysis of the flavour structure of dimension-6 effective field theory (EFT) operators in multilepton final states is presented, focusing on the interactions involving Z bosons. For the first time, the flavour structure of these operators is disentangled by simultaneously probing the interactions with different quark generations. The analysis targets the associated production of a top quark pair and a Z boson, as well as diboson processes in final states with at least three leptons, which can be electrons or muons. The data were recorded by the CMS experiment in the years 2016$-$2018 in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb$^{-1}$. Consistency with the standard model of particle physics is observed and limits are set on the selected Wilson coefficients, split into couplings to light- and heavy-quark generations.
Summary of the limits obtained for the Wilson coefficients.
Likelihood scan of cHqMRe1122 versus cHqMRe33. Other Wilson coefficients are fixed to zero.
Likelihood scan of cHq3MRe1122 versus cHq3MRe33. Other Wilson coefficients are fixed to zero.
Constraints on the Wilson coefficients (WCs) corresponding to dimension-six operators of the standard model effective field theory (SMEFT) are determined from a simultaneous fit to seven sets of CMS measurements probing Higgs boson, electroweak vector boson, top quark, and multi-jet production. The measurements of the electroweak precision observables at LEP and SLC are also included and provide complementary constraints to those from CMS. The CMS measurements, using $36$-$138\,\mathrm{fb}^{-1}$ of LHC proton-proton collision data at $\sqrt{s}=13\,\mathrm{TeV}$, are chosen to provide sensitivity to a broad set of operators, for which consistent SMEFT predictions can be derived. These are primarily measurements of differential cross sections or, in the case of Higgs boson production, simplified template cross sections, which are subsequently parametrized in the WCs. Measurements targeting $\mathrm{t\bar{t}X}$ production model the SMEFT effects directly in the reconstructed observables. Individual constraints on 64 WCs, and constraints on 42 linear combinations of WCs, are obtained. In the case of the linear combinations, the 42 parameters are varied simultaneously.
Expected and observed 95% CL limits on linear combinations of Wilson coefficients from the hybrid fit with the full set of input measurements.
Expected and observed individual 95% CL limits on Wilson coefficients from the hybrid fit with the full set of input measurements.
Rotation matrix obtained by performing the PCA on the Hessian matrix of the full set of measurements, including the t(t)X analysis.
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