Top, Higgs, diboson and electroweak fit to the Standard Model effective field theory

John Ellis,Tevong You,Veronica Sanz,Ken Mimasu,Maeve Madigan

doi:10.1007/jhep04(2021)279

Abstract

The search for effective field theory deformations of the Standard Model (SM) is a major goal of particle physics that can benefit from a global approach in the framework of the Standard Model Effective Field Theory (SMEFT). For the first time, we include LHC data on top production and differential distributions together with Higgs production and decay rates and Simplified Template Cross-Section (STXS) measurements in a global fit, as well as precision electroweak and diboson measurements from LEP and the LHC, in a global analysis with SMEFT operators of dimension 6 included linearly. We present the constraints on the coefficients of these operators, both individually and when marginalised, in flavour-universal and top-specific scenarios, studying the interplay of these datasets and the correlations they induce in the SMEFT. We then explore the constraints that our linear SMEFT analysis imposes on specific ultra-violet completions of the Standard Model, including those with single additional fields and low-mass stop squarks. We also present a model-independent search for deformations of the SM that contribute to between two and five SMEFT operator coefficients. In no case do we find any significant evidence for physics beyond the SM. Our underlying Fitmaker public code provides a framework for future generalisations of our analysis, including a quadratic treatment of dimension-6 operators.

Highlights

A more general EFT parametrisation in which the electroweak SU(2)×U(1) symmetry is non-linearly realised and the Higgs is added as a singlet scalar, known as the Higgs EFT (HEFT), is described, e.g., in ref. [75] with fits given in refs. [76,77,78]
The global analysis we present here is performed at linear order in the Standard Model Effective Field Theory (SMEFT) operator coefficients
In the top panel we show how these operators are constrained in the cases of four specific UV models from table 3: S, φ [which may be derived from a 2-Higgs Doublet Model (2HDM)], Q1 &Q7 and B&B1, showing a detail in the inset

Summary

Introduction

A more general EFT parametrisation in which the electroweak SU(2)×U(1) symmetry is non-linearly realised and the Higgs is added as a singlet scalar, known as the Higgs EFT (HEFT), is described, e.g., in ref. [75] with fits given in refs. [76,77,78]. When such states are produced on shell, factorising a given process into production and decay via the narrow-width approximation (NWA) allows the decay contributions to be computed separately, added to the prediction If these effects cannot be factorised, as in the case of W -mass modifications or off-shell vector bosons in Higgs decays, the aX i are obtained by generating the predictions over a range of coefficient values and numerically fitting for the linear dependence. JHEP04(2021)279 the measured decay channel (usually leptonic for W and Z) This choice is not expected to have a significant impact on the results, given that top data is mainly sensitive to top-related operators, with those that modify gauge or Higgs boson decays being better constrained elsewhere. This issue might be mitigated by including quadratic terms in the SMEFT expansion, but an analysis of this possibility lies beyond the scope of the present analysis

Summary and conclusions

Findings

Tables of numerical fit results