Measurements of Higgs boson production via gluon-gluon fusion and vector-boson fusion using $H\rightarrow WW^\ast \rightarrow \ellν\ellν$ decays in $pp$ collisions with the ATLAS detector and their effective field theory interpretations

TL;DR

This ATLAS analysis measures Higgs production in the H→WW* channel via gluon-gluon fusion and vector-boson fusion using Run 2 LHC data at √s=13 TeV, achieving 12.4^{+1.3}_{-1.2} pb for ggF and 0.79^{+0.18}_{-0.16} pb for VBF cross-sections times B(H→WW*), consistent with SM predictions. The study employs a Detailed STXS framework with 15 fiducial categories and introduces a CP-sensitive STXS_CP scheme to probe CP-odd operators, using Δφjj± as the key CP-sensitive observable. It performs SMEFT interpretations in both CP-conserving and CP-violating scenarios, parameterising cross-sections and widths with Wilson coefficients and applying principal component analysis to stabilize the fit. The results exhibit improved STXS precision over previous analyses, constrain 16 d=6 operators, and show no evidence for beyond-SM CP violation within the current sensitivity, illustrating the SM’s robustness in Higgs interactions at high precision.

Abstract

Higgs boson production cross-sections via gluon-gluon fusion and vector-boson fusion in proton-proton collisions are measured in the $H\rightarrow WW^\ast \rightarrow \ellν\ellν$ decay channel. The Large Hadron Collider delivered proton-proton collisions at a centre-of-mass energy of $13\,\textrm{TeV}$ between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of $140\,\textrm{fb}^{-1}$. The total cross-sections for Higgs boson production by gluon-gluon fusion and vector-boson fusion times the $H\rightarrow WW^\ast$ branching ratio are measured to be $12.4^{+1.3}_{-1.2}\,\textrm{pb}$ and $0.79^{+0.18}_{-0.16}\,\textrm{pb}$, respectively, in agreement with the Standard Model predictions. Higgs boson production is further characterised through measurements of Simplified Template Cross-Sections in a total of fifteen kinematic fiducial regions. A new scheme of kinematic fiducial regions has been introduced to enhance the sensitivity to CP-violating effects in Higgs boson interactions. Both schemes are used to constrain CP-even and CP-odd dimension-six operators in the Standard Model effective field theory.

Figures (25)

• Figure 1: Multiplicity distributions for jets with $\pt > \qty{30}{\text{Ge V}\xspace}$ and $|\eta| < 4.5$ in the DF channel, (left) after applying the preselection criteria and (right) after additionally vetoing events containing at least one using the 85% efficiency working point for jets with $\pt > \qty{20}{\text{Ge V}\xspace}$ and $|\eta| < 2.5$. Shown are pre-fit distributions (see Section \ref{['sec:results']} for its definition), assuming SM Higgs boson production. The very thin hatched band represents the small statistical uncertainty of the samples relative to their yields. The expected ggF (VBF) signal contribution is additionally overlaid and scaled up by a factor of 70 (700) for visibility.
• Figure 2: Two sets ('Production mode' and 'Reduced STXS 1.2') of exclusive phase-space regions ('production categories') defined at particle-level for (left panel, shaded) the measurement of the Higgs boson production cross-sections and (right panel, blank) the corresponding reconstructed SRs. The description of the production categories and reconstructed SRs is given in Section \ref{['sec:channels']}. All Reduced STXS 1.2 production categories include a requirement on the Higgs boson rapidity of $|y_H| < 2.5$. Single lines indicate SRs that exist in only the DF channel; double lines indicate SRs that exist in both the DF and SF channels. The colours of each SR box indicate the SM expected relative fractions of ggF (blue, left part of each SR box) and VBF (orange, right part of each SR box). In cases where a SF SR is present, its box is shown beneath the corresponding DF SR box.
• Figure 3: Relative SM signal composition in terms of the measured STXS production categories for each reconstructed SR. The phase space selections based on $\pt^{\ell\ell,\textrm{miss}}$ and $m_{jj}$ summarised on the right are described in Section \ref{['sec:stxs_cat']}. The signal purity ('Sig. / Tot.') is defined as the sum of the yields for the measured STXS production categories, i.e. all those shown in the legend, divided by the sum of the yields for all physics processes. For each SR, the $gg\xspace H\xspace$ contributions start on the left, going from lighter to darker shades, followed by the EW $qqH\xspace$, again going from lighter to darker shades.
• Figure 4: $\mathrm{STXS}_{\textrm{CP}}$ categorisation scheme, modified from the Stage 1.2 STXS categorisation scheme shown in Figure \ref{['fig:STXS_cat']}, showing (left panel, shaded) the particle-level production categories and (right panel, blank) the corresponding reconstructed SRs. The description of the production categories and reconstructed SRs is given in Section \ref{['sec:channels']}. All production categories in the $\mathrm{STXS}_{\textrm{CP}}$ categorisation scheme include a requirement on the Higgs boson rapidity of $|y_H| < 2.5$. The $gg\xspace H\xspace$ 0/1-jet $200 \leq \pT^H\xspace < \qty{300}{\text{Ge V}\xspace}$ and $\pT^H\xspace \geq \qty{300}{\text{Ge V}\xspace}$ categories branch off of the ggF 1-jet line to avoid complicating the figure. Single lines indicate SRs that exist in only the DF channel; double lines indicate SRs that exist in both the DF and SF channels. The colours of each SR box indicate the SM expected relative fractions of ggF (blue, left part of each SR box) and VBF (orange, right part of each SR box). In cases where a SF SR is present, its box is shown beneath the corresponding DF SR box. The pale blue and orange boxes indicate production categories and SRs that are unchanged from the Stage 1.2 STXS categorisation scheme.
• Figure 5: Yield distributions in the CRs of the STXS measurement after a full fit to data (i.e., 'Post-fit'). The vertical dashed lines delineate CRs targeting different backgrounds, where '$\PZ/\gamma^{*}\xspace\xspace\to\ell\ell$' corresponds to '$\PZ/\gamma^{*}\xspace\xspace\to ee/\mu\mu\xspace$'. The middle panel shows the ratio of the data to the sum of the fitted signal and background, and the bottom panel shows the relative composition among the fitted signal and background processes. In the top and middle panels, the hatched band shows the total uncertainty, including both statistical and systematics sources.