Constraints on effective field theories via quadruple-differential angular decay rates from $t$-channel single-top-quark production at $\sqrt{s}=13$ TeV with the ATLAS detector

Events with $t$-channel single top quarks are used to probe effective field theory operators in $\sqrt{s}=13$ TeV proton-proton collision data corresponding to 140 fb${}^{-1}$ recorded by the ATLAS detector at the Large Hadron Collider. An analysis method leveraging Fourier techniques applied to quadruple-differential decay rates based on observables containing angular information about the decays of the top quarks is used to achieve high sensitivity. The relevant effective field theory operators are those sensitive to top-quark decay and $t$-channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions.