Dijet bounds on third-generation four-quark operators

TL;DR

The paper analyzes dijet angular distributions to constrain ten third-generation four-quark SMEFT operators, showing that RG evolution with leading-log contributions up to two loops renders all ten operators testable at the LHC. Tree-level sensitivity exists only for five bottom-quark operators, while RG-induced mixing allows probing the remaining operators, with the strongest bounds obtained for the bottom-quark set. The analysis highlights significant RG effects, particularly for operators involving $Q^{(8)}_{Qb}$, and demonstrates that, at high $M_{jj}$, constraints are dominated by quadratic BSM contributions, implying sensitivity to dimension-eight SMEFT deformations. These results emphasize the importance of including RG-induced mixing when interpreting high-energy collider data in SMEFT and inform UV-model implications for third-generation four-quark interactions.

Abstract

We use dijet measurements from the Large Hadron Collider to constrain ten third-generation four-quark operators in the Standard Model effective field theory. At tree level, only the five operators involving four bottom quarks are directly constrained, but renormalization group (RG) effects allow all ten operators to be probed. Our analysis includes the dominant leading-logarithmic RG contributions up to two-loop order. The resulting bounds for the first five operators are nominal stronger or comparable to current limits, while those for the remaining operators remain weak despite the inclusion of logarithmically enhanced corrections.

Figures (3)

• Figure 1: Left: Example of a QCD penguin diagram. Right: Example of a QCD double-penguin diagram. The red boxes indicate operator insertions. The leading UV poles of these diagrams determine, respectively, the one-loop logarithmic and two-loop double-logarithmic corrections in the SMEFT RG flow of the third-generation four-quark operators. See main text for more details.
• Figure 2: Normalized $\chi$ distributions in the two lowest mass bins considered in the CMS analysis CMS:2018ucw. The SM predictions obtained by CMS, including NLO QCD and EW corrections, are shown as black dotted lines. Error bars denote the statistical and experimental systematic uncertainties added in quadrature, while the gray band represents the theoretical uncertainties. For comparison, the normalized dijet angular distributions for $C^{(8)}_{Qb}(\Lambda) = 20/{\rm TeV}^2$ and $C_{tt}(\Lambda) = 500/{\rm TeV}^2$ are shown as red lines in the left- and right-hand panels, respectively. The lower panels display the ratios ($R$) of the unfolded data to the SM predictions, together with the corresponding BSM distributions. Additional explanations can be found in the main text.
• Figure 3: $95\%$ CL limits on all possible pairs of third-generation four-quark operators involving four bottom-quark fields. The solid (dotted) red contours show the constraints on the corresponding Wilson coefficients evaluated at $v = 250 \, {\rm GeV}$ ($\Lambda = 10 \, {\rm TeV}$). The black point in each of the ten panels represents the SM. Additional details can be found in the main text.