Study of $(W/Z)H$ production and Higgs boson couplings using $H \rightarrow WW^{\ast}$ decays with the ATLAS detector

TL;DR

This ATLAS study searches for Higgs production in association with W or Z bosons with H→WW*, using 7 and 8 TeV LHC data. Four VH topologies (4l, 3l, 2l OS, 2l SS) are analyzed with multiple signal and control regions, and a profile-likelihood fit extracts VH signal yields while constraining backgrounds. The VH signal strength is measured as μ_VH = 3.0^{+1.3}_{-1.1}(stat)^{+1.0}_{-0.7}(sys), and a combined VH+ggF+VBF analysis yields an overall significance of $Z_0=6.5$ for H→WW*, with a total signal strength μ = 1.16^{+0.16}_{-0.15}(stat)^{+0.18}_{-0.15}(sys). Interpreting the results in the κ framework gives |κ_V| = 1.06^{+0.10}_{-0.10} and |κ_F| = 0.85^{+0.26}_{-0.20}, supporting SM-like Higgs couplings within uncertainties. The analysis demonstrates VH-channel sensitivity to Higgs couplings and provides robust cross-checks via combination with ggF and VBF channels through H→WW* decays.

Abstract

A search for Higgs boson production in association with a $W$ or $Z$ boson, in the $H \rightarrow WW^{\ast}$ decay channel, is performed with a data sample collected with the ATLAS detector at the LHC in proton-proton collisions at centre-of-mass energies $\sqrt{s}=7$ TeV and 8 TeV, corresponding to integrated luminosities of 4.5 ${\rm fb}^{-1}$ and 20.3 ${\rm fb}^{-1}$, respectively. The $WH$ production mode is studied in two-lepton and three-lepton final states, while two-lepton and four-lepton final states are used to search for the $ZH$ production mode. The observed significance, for the combined $WH$ and $ZH$ production, is 2.5 standard deviations while a significance of 0.9 standard deviations is expected in the Standard Model Higgs boson hypothesis. The ratio of the combined $WH$ and $ZH$ signal yield to the Standard Model expectation, $μ_{VH}$, is found to be $μ_{VH} =3.0^{+1.3}_{-1.1}{\, {(\rm stat.)}}^{+1.0}_{-0.7}{\,{(\rm sys.)}}$ for the Higgs boson mass of 125.36 GeV. The $WH$ and $ZH$ production modes are also combined with the gluon fusion and vector boson fusion production modes studied in the $H \to WW^* \to \ell ν\ell ν$ decay channel, resulting in an overall observed significance of 6.5 standard deviations and $μ_{\rm ggF+VBF+VH} = 1.16^{+0.16}_{-0.15} {\rm (stat.)}^{+0.18}_{-0.15} {\rm (sys.)}$. The results are interpreted in terms of scaling factors of the Higgs boson couplings to vector bosons ($κ_V$) and fermions ($κ_F$); the combined results are: $|κ_V| = 1.06^{+0.10}_{-0.10}$, $|κ_F| = 0.85^{+0.26}_{-0.20}$.

Figures (12)

• Figure 1: Tree-level Feynman diagrams of the $VH(H{\rightarrow\,}WW^{\ast})$ topologies studied in this analysis: (a) ${\rm 4}{\ell}$ channel (b) ${\rm 3}{\ell}$ channel (c) opposite-sign ${\rm 2}{\ell}$ channel and (d) same-sign ${\rm 2}{\ell}$ channel. For charged lepton external lines, the directions of arrows refer to the superscripted sign. Relevant arrows are assigned to the associated neutrino external lines.
• Figure 2: Distributions of the invariant mass of leptons $\ell_0$ and $\ell_2$, defined in secton \ref{['sec:analysis']}, in the five CRs defined in the 3$\ell$ channel: (a) 3$\ell$-$WZ$ CR, (b) 3$\ell$-$ZZ$ CR, (c) 3$\ell$-$Z$jets CR, (d) 3$\ell$-Top CR and (e) 3$\ell$-$Z\gamma$ CR. Data (points) are compared to the background plus $VH(H{\rightarrow\,}WW^{\ast})$ (=125 ) signal expectation (stacked filled histograms), where the background contributions are normalised by applying the normalisation factors shown in table \ref{['tab:NFs']}. The hatched area on the histogram represents total uncertainty, both statistical and systematic (see section \ref{['sec:systematics']}), on the total background estimate. The last bin includes overflows.
• Figure 3: Distribution of the 4-lepton invariant mass $m_{4\ell}$ in the 4$\ell$-$ZZ$ CR control region. Data (points) are compared to the background plus $VH(H{\rightarrow\,}WW^{\ast})$ (=125 ) signal expectation (stacked filled histograms), where $ZZ^{\ast}$ events are normalised by applying the normalisation factor shown in table \ref{['tab:NFs']}. The hatched area on the histogram represents total uncertainty, both statistical and systematic (see section \ref{['sec:systematics']}), on the total background estimate. The last bin includes overflows.
• Figure 4: Distributions of the difference in rapidity between the two leading jets $\Delta y_{jj}$ (a) in the 2$\ell$-OSTop CR and (b) in the 2$\ell$-$Z\tau\tau$ CR. Data (points) are compared to the background plus $VH(H{\rightarrow\,}WW^{\ast})$ (=125 ) signal expectation (stacked filled histograms), where the background contributions are normalised by applying the normalisation factors shown in table \ref{['tab:NFs']}. The hatched area on the histogram represents total uncertainty, both statistical and systematic (see section \ref{['sec:systematics']}), on the total background estimate. The last bin includes overflows.
• Figure 5: Distribution of relevant variables in the control regions in the 2$\ell$-SS channel: (a) azimuthal angle between the two leptons $\Delta \phi_{\ell_1\ell_2}$ in the 2$\ell$-$W\gamma$ CR, (b) transverse momentum of the leading lepton in the 2$\ell$-$WZ$ CR, (c) transverse mass $m_{\rm T}$ in the 2$\ell$-$WW$ CR, (d) missing transverse momentum $\met$ in the 2$\ell$-SSTop CR and (e) $\Delta \phi_{\ell_1\ell_2}$, in the 2$\ell$-$Z$jets CR. Data (points) are compared to the background plus $VH(H{\rightarrow\,}WW^{\ast})$ (=125 ) signal expectation (stacked filled histograms), where the background contributions are normalised by applying the normalisation factors shown in table \ref{['tab:NFs']}. The hatched area on the histogram represents total uncertainty, both statistical and systematic (see section \ref{['sec:systematics']}), on the total background estimate. The last bin includes overflows.