Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

TL;DR

ATLAS analyzes Higgs properties using diboson decays H→γγ, ZZ*→4ℓ, and WW*→ℓνℓν with ~25 fb⁻¹ at 7 and 8 TeV. A comprehensive, category-driven analysis achieves evidence for vector-boson fusion and performs global fits to Higgs couplings, including loop-induced processes, via profile-likelihood methods. The results show Higgs mass and production strengths consistent with the Standard Model, while constraining custodial symmetry and potential BSM contributions in loops. The work provides the most precise multi-channel Higgs property measurements to that date and strengthens the SM Higgs boson interpretation in the diboson sector.

Abstract

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, $H\rightarrowγγ$, $H\rightarrow ZZ^{*}\rightarrow 4 \ell$ and $H\rightarrow W W \rightarrow \ellν\ellν$. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of about 25 fb$^{-1}$. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson.

Figures (13)

• Figure 1: Distribution of the VBF BDT response after applying the selection of the inclusive analysis and requiring in addition the presence of two jets with $|\Delta\eta_{jj}| > 2$ and $|\eta^*|<5$. The data in the signal sidebands ( i.e. excluding the $m_{\gamma\gamma}$ region 120--130 GeV), the expected background, and the expected signal from VBF and ggF production are shown. They are all normalised to unity except ggF, which is normalised to the ratio between the numbers of ggF and VBF events passing the selection described above.
• Figure 2: Invariant mass distribution of diphoton candidates after all selections of the inclusive analysis for the combined 7 TeV and 8 TeV data. The result of a fit to the data with the sum of a SM Higgs boson signal (with $m_H=126.8$Ge V and free signal strength) and background is superimposed. The residuals of the data with respect to the fitted background are displayed in the lower panel.
• Figure 3: The distribution of the four-lepton invariant mass, $m_{4\ell}$, for the selected candidates in the data. The estimated background, as well as the expected SM Higgs boson signal for $m_H=124.3\,\mathrm{\ Ge V} \textrm{Ge V}$ (scaled by the signal strength obtained from fits to the data), are also shown. The single-resonant peak at $m_{4\ell}\sim$ 90 GeV includes contributions from $s$-channel $Z/\gamma^*$ and $t$-channel $(Z^*/\gamma^*)(Z^*/\gamma^*)$ production.
• Figure 4: The $m_{\ell\ell}$ distribution of $e\mu$ events with $N_\textrm{jet}\,{=}\,0$ for the 8 TeV $H{\rightarrow\,}WW^{*}{\rightarrow\,}\ell\nu\ell\nu$ analysis. The events with $m_{\ell\ell} < 50\mathrm{\ Ge V} \textrm{Ge V}$ correspond to the signal region except that the $\Delta\phi_{\ell\ell}\xspace < 1.8$ requirement is not applied here, and the events with $50\mathrm{\ Ge V} \textrm{Ge V} < m_{\ell\ell} < 100\mathrm{\ Ge V} \textrm{Ge V}$ correspond to the $N_\textrm{jet}\,{=}\,0$$WW$ control region. The signal is stacked on top of the background. The hatched area represents the total uncertainty on the sum of the signal and background yields from statistical, experimental, and theoretical sources. The lower part of the figure shows the ratio of the data to the predicted background. For comparison, the expected ratio of the signal plus background to the background alone is also shown.
• Figure 5: The transverse mass distributions for events passing the full selection of the $H{\rightarrow\,}WW^{*}{\rightarrow\,}\ell\nu\ell\nu$ analysis: (a) summed over all lepton flavours for final states with $N_\textrm{jet}\,{\le}\,1$; (b) different-flavour final states with $N_\textrm{jet}\,{\ge}\,2$. The signal is stacked on top of the background, and in (b) is shown separately for the ggF and VBF production processes. The hatched area represents the total uncertainty on the sum of the signal and background yields from statistical, experimental, and theoretical sources. In the lower part of (a), the residuals of the data with respect to the estimated background are shown, compared to the expected $m_{\rm T}$ distribution of a SM Higgs boson.