Constraining the four-light quark operators in the SMEFT with multijet and VBF processes at linear level
Céline Degrande, Matteo Maltoni
TL;DR
This work constrains ten four-light-quark SMEFT operators by studying their interference with the SM in multijet and VBF-like processes at LO, across multijet, Z+jets, W+jets, and γ+jets channels. The analysis uses a MadGraph5_aMC@NLO framework with a dedicated 4LQ UFO model, MLM matching for up to three jets, and Pythia8 parton showering, evaluating differential observables to identify the most sensitive directions in the operator space. By constructing a χ^2 that combines SM, interference, and potential quadratic contributions, the authors extract both individual and marginalised bounds, finding that the direction associated with $C_{qq}^{(3)}/\Lambda^2$ is typically best constrained, with multijet data providing the strongest limits. They highlight that, at current energies, the $O(1/\Lambda^4)$ squared terms are often comparable to or dominate over the linear interference, emphasizing the need to account for quadratic effects and to improve SM predictions and observable sensitivity for tighter SMEFT constraints.
Abstract
We investigate how the interference of the SM with ten four-light quark operators in the SMEFT can be constrained thanks to multijet and $Z,W,γ$ VBF production in association with jets. The differential distributions for each process are generated at LO for different jet multiplicities, that are then merged and showered. We check which observables provide better bounds on the Wilson coefficients, and what directions in the ten-dimensional coefficient space they are able to probe. We discuss the relevance of the quadratic contributions with respect to the linear terms.