Updated Global SMEFT Fit to Higgs, Diboson and Electroweak Data

TL;DR

This study performs a comprehensive global SMEFT fit to precision electroweak data, LEP WW measurements, and Higgs+diboson data from LHC Run 1 and Run 2, considering 20 dimension-6 operators in both the Warsaw and SILH bases. Using a linear EFT framework and SMEFTsim predictions, the authors show that Run 2 data substantially improve constraints, though the best-fit values remain consistent with the Standard Model and no significant BSM signal is detected. They map the operator constraints to various BSM scenarios, including tree-level extensions and MSSM stop loops, illustrating that indirect SMEFT bounds can be competitive with, or even surpass, direct search limits in certain regions. The results highlight the synergy between precision EW, diboson, and Higgs data, and emphasize the value of differential information (STXS, high-$p_T$ tails) for future SMEFT analyses.

Abstract

The ATLAS and CMS collaborations have recently released significant new data on Higgs and diboson production in LHC Run 2. Measurements of Higgs properties have improved in many channels, while kinematic information for $h \to γγ$ and $h \to ZZ$ can now be more accurately incorporated in fits using the STXS method, and $W^+ W^-$ diboson production at high $p_T$ gives new sensitivity to deviations from the Standard Model. We have performed an updated global fit to precision electroweak data, $W^+W^-$ measurements at LEP, and Higgs and diboson data from Runs 1 and 2 of the LHC in the framework of the Standard Model Effective Field Theory (SMEFT), allowing all coefficients to vary across the combined dataset, and present the results in both the Warsaw and SILH operator bases. We exhibit the improvement in the constraints on operator coefficients provided by the LHC Run 2 data, and discuss the correlations between them. We also explore the constraints our fit results impose on several models of physics beyond the Standard Model, including models that contribute to the operator coefficients at the tree level and stops in the MSSM that contribute via loops.

Figures (8)

• Figure 1: Fits to the $\Delta S$ and $\Delta T$ parameters Kennedy:1988snHoldom:1990tcGolden:1990igAltarelli:1990zdGrinstein:1991cdPeskin:1991sw using $Z$-pole, $W$ mass, and LEP 2 $WW$ scattering measurements (red), using LHC Run 1 and Run 2 Higgs results (dark yellow), and all the data (blue). The darker and lighter shaded regions are allowed at 1 and 2$\sigma$, respectively. We see that the Higgs measurements at the LHC have similar impacts to the electroweak precision measurements, and are largely complementary, emphasizing the need for a combined global fit.
• Figure 2: Results from global fits in the Warsaw basis (orange) including all operators simultaneously (upper panel) and switching each operator on individually (lower panel). Also shown are fits omitting the LHC Run 2 data (blue). We display the best-fit values and 95% CL ranges.
• Figure 3: Results from global fits in the SILH basis (orange) including all operators simultaneously (upper panel) and switching each operator on individually (lower panel). Also shown are fits to the precision electroweak $Z$-pole and $W$-mass data (green) and results from Ellis:2014jta (blue). We display the best-fit values and 95% CL ranges.
• Figure 4: The relative improvement in the standard deviations of the Wilson coefficients in the Warsaw basis when LHC Run 2 data are added to the fits (a lower number correspond to more improvement). The upper and lower panels correspond to when all operators are included simultaneously or when switching on each operator individually, respectively.
• Figure 5: Matrices of correlations among the operator coefficients in the Warsaw (left) and SILH (right) bases, as shown in Table \ref{['tab:global']}, using the colour code shown on the right.