Combination of measurements of CP properties of Higgs boson interactions with vector bosons using proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Abstract

A combination of measurements of the CP properties of Higgs boson interactions with electroweak gauge bosons is presented, using 140 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded by the ATLAS detector. Results from $H\toττ$, $H\to WW^{*}$, $H\toγγ$, $H\to ZZ^{*}$, and $WH,H\to b\bar{b}$ channels are combined. No evidence of CP violation is observed, and constrains on the CP-violating operators in the SMEFT framework are set in the Warsaw basis. The results from the combination improve by over 40% on previous individual limits on $c_{H\tilde{W}}$ and, for the first time, simultaneous constraints on three coefficients $c_{H\tilde{W}}$, $c_{H\tilde{B}}$, and $c_{H\tilde{W}B}$ are set. This limits are the most stringent constraints to date on the relevant Wilson coefficients in the SMEFT framework with minimum model dependence.

Figures (6)

• Figure 1: Measured $WH$ production cross-sections times the $W\rightarrow \ell \nu$ and the $H \rightarrow b\bar{b}$ branching ratios normalized to their SM predictions. The best fit values and corresponding uncertainties (total as well as its statistical and systematic components) are shown for all regions. Theoretical uncertainties on the predictions are not shown as they are too small to be visible.
• Figure 2: Negative profile log-likelihood ratio scans are shown as a function of $c_{H\tilde{W}}$, with single-parameter fits ($c_{H\tilde{B}}$ = $c_{H\tilde{W}B}$ = 0) and simultaneous fits (all three coefficients floating), for (a) linear-only and (b) linear plus quadratic terms. Solid lines indicate the observed scans, while dashed lines show the expected results. The dashed horizontal lines show the thresholds defining the 68% and 95% confidence intervals, assuming the asymptotic approximation.
• Figure 3: The observed 68% (dashed line) and 95% (solid line) CL two-dimensional contours are shown for all three pairings of the Warsaw basis: (a, d) $c_{H\tilde{W}}$ versus $c_{H\tilde{B}}$, (b, e) $c_{H\tilde{W}}$ versus $c_{H\tilde{W}B}$, and (c, f) $c_{H\tilde{B}}$ versus $c_{H\tilde{W}B}$ a simultaneous fit, for (a, b, c) linear-only and (d, e, f) linear plus quadratic terms interpretations. Expected contour lines are also shown. All couplings scale as $1/\Lambda^2$ with $\Lambda = 1$$\text{Te V}$.
• Figure 4: Best-fit values and 95% CL intervals for all three Wilson coefficients obtained in a simultaneous fit to all coefficients. In both cases, linear and linear plus quadratic scenarios are shown. Expected limits using the full model and statistical-only are also presented.
• Figure 5: Observed negative log-likelihood ratio ($2\Delta\text{NLL}\xspace$) scans as a function of $c_{H\tilde{W}}$ considering the (a) linear-only and the (b) linear plus quadratic terms for the individual channels (in different colors) and their combination. The dashed horizontal lines show the values of $\Delta\text{NLL}$ thresholds defining the 68% and 95% confidence intervals, assuming the asymptotic approximation.