Abstract
We study the forward-backward asymmetry AFB in pp → ℓ+ℓ− at the Z peak within the Standard Model Effective Field Theory (SMEFT). We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks, which close a flat direction in the electroweak precision SMEFT fit. Moreover, we show that current AFB data is precise enough so that its inclusion in the fit improves significantly LEP bounds even in simple New Physics setups. This demonstrates that the LHC can compete with and complement LEP when it comes to precision measurements of the Z boson properties.
Highlights
Guidelines for subsequent discoveries of the remaining SM degrees of freedom: the top quark and the Higgs boson
Correus 22085, E-46071 València, supported by the Generalitat Valenciana (Spain) bCNRS/IN2P3, IJCLab, Université Paris-Saclay, 91405 Orsay, France E-mail: vicbreso@ific.uv.es, adam.falkowski@cern.ch, martin.gonzalez@ific.uv.es Abstract: We study the forward-backward asymmetry AFB in pp → + − at the Z peak within the Standard Model Effective Field Theory (SMEFT)
We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks, which close a flat direction in the electroweak precision SMEFT fit
Summary
The SMEFT Lagrangian [1, 2] is organized into an expansion in 1/Λ2, where Λ is interpreted as the mass scale of new particles in the UV completion of this EFT. − gL2 + gY2 Zμ fLγμ((Tf3 − s2θQf ) I + δgLZf )fL f ∈u,d,e,ν fRγμ(−s2θQf I + δgRZf )fR In this Lagrangian, the SM fermion fields f are 3-vectors in the flavor space, written in the basis where their mass terms are diagonal (for neutrinos, where their charged current interactions are diagonal in the limit δgLW e → 0), s2θ = gY2 /(gY2 + gL2 ) is the sine squared of the weak mixing angle and V is the unitary CKM matrix. Deformations of these interactions due to the dimension-6 operators are parametrized by the vertex corrections δg, which are 3 × 3 matrices in the flavor space and can be flavor-violating They can be expressed as linear combinations of. In appendix A we provide the map relating δg to the Wilson coefficients of the commonly used Warsaw basis [25]
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