Measurement of differential and integrated fiducial cross sections for Higgs boson production in the four-lepton decay channel in pp collisions at sqrt(s) = 7 and 8 TeV

TL;DR

The paper presents CMS measurements of integrated and differential fiducial cross sections for Higgs boson production in the H→4l channel at √s = 7 and 8 TeV, defined in a fiducial phase space to reduce model dependence. An unbinned maximum-likelihood fit to the four-lepton mass spectrum, coupled with a detector response matrix, extracts cross sections and accounts for backgrounds, including a Z→4l control channel and its ratio to H→4l. Results show consistency with SM NNLL+NNLO predictions, with large statistical uncertainties, and provide validation of Higgs production modelling via differential observables such as jet activity and H system kinematics. A mass-difference analysis between H and Z yields Δm ≈ 34.2 GeV, implying m_H ≈ 125.4 GeV, corroborating existing Higgs mass measurements. Overall, the study validates SM Higgs production in the four-lepton channel and demonstrates a robust fiducial-cross-section methodology with controlled systematic effects.

Abstract

Integrated fiducial cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at sqrt(s) = 7 and 8 TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 inverse femtobarns at 7 TeV, and 19.7 inverse femtobarns at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are measured using the 8 TeV data, and are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z to 4l cross section, and its ratio to the H to 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. The integrated H to 4l fiducial cross section is measured to be 0.56 +0.67-0.44 (stat) +0.21-0.06 (syst) fb at 7 TeV, and 1.11 +0.41-0.35 (stat) +0.14-0.10 (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.

Figures (5)

• Figure 1: Distributions of the $m_{4\ell}$ observable in 7$\,\text{Te\spaceV}$ (left) and 8$\,\text{Te\spaceV}$ (right) data, as well as expectations for the SM Higgs boson ($m_{{H}\xspace}=125.0\,\text{Ge\spaceV}\xspace$) and other contributing SM processes, including resonant ${Z}\xspace \to 4\ell\xspace$ decays.
• Figure 2: Observed inclusive four-lepton mass distribution and the resulting fits of the signal and background models, presented in Section \ref{['sec:Methodology']}, in case of an independent ${H}\xspace \to 4\ell\xspace$ fit (left) and a simultaneous ${H}\xspace \to 4\ell\xspace$ and ${Z}\xspace \to 4\ell\xspace$ fit (right). The ${g}\xspace{g}\xspace \to {H}\xspace \to 4\ell$ process is modelled using Powheg+JHUGen, while ${q}\xspace \overline{{q}}\xspace \to 4\ell$ process is modelled using powheg (both $s$- and $t$/$u$-channels). The sub-dominant component of the Higgs boson production is denoted as XH = VBF + $\mathrm{V} {H}\xspace$ + ${t}\xspace \overline{{t}}\xspace {H}\xspace\xspace$.
• Figure 3: Results of measurements of the integrated ${H}\xspace \to 4\ell\xspace$ fiducial cross section in pp collisions at 7 and 8$\,\text{Te\spaceV}$, with a comparison to SM estimates. The red error bar represents the systematic uncertainty, while the black error bar represents the combined statistical and systematic uncertainties, summed in quadrature. The additional systematic effect associated with model dependence is represented by grey boxes. The theoretical estimates at NNLL+NNLO accuracy and the corresponding systematic uncertainties are shown in blue as a function of the centre-of-mass energy. The acceptance of the dominant ${g}\xspace {g}\xspace \to {H}\xspace\xspace$ contribution is modelled at the parton level using HRes, and corrected for hadronization and underlying-event effects estimated using Powheg+JHUGen and Pythia 6.4.
• Figure 4: Results of the differential ${H}\xspace \to 4\ell\xspace$ fiducial cross section measurements and comparison to the theoretical estimates for the transverse momentum (left) and the rapidity (right) of the four-lepton system. The red error bars represent the systematic uncertainties, while black error bars represent the combined statistical and systematic uncertainties, summed in quadrature. The additional systematic uncertainty associated with the model dependence is separately represented by the grey boxes. Theoretical estimates, in which the acceptance of the dominant ${g}\xspace {g}\xspace \to {H}\xspace\xspace$ contribution is modelled by Powheg+JHUGen+pythia, Powheg MiNLO HJ+pythia, and HRes generators as discussed in Section \ref{['sec:DatasetsSimulationPAS']}, are shown in blue, brown, and pink, respectively. The sub-dominant component of the signal XH is indicated separately in green. In all estimations the total cross section is normalized to the SM estimate computed at NNLL+NNLO accuracy. Systematic uncertainties correspond to the accuracy of the generators used to derive the differential estimations. The bottom panel shows the ratio of data or theoretical estimates to the HRes theoretical estimations.
• Figure 5: Results of the differential ${H}\xspace \to 4\ell\xspace$ fiducial cross section measurements and comparison to the theoretical estimates for the transverse momentum of the leading jet (top left), separation in rapidity between the Higgs boson candidate and the leading jet (top right), as well as for the jet multiplicity (bottom). The red error bars represent the systematic uncertainties, while black error bars represent the combined statistical and systematic uncertainties, summed in quadrature. The additional systematic uncertainty associated with the model dependence is separately represented by the grey boxes. Theoretical estimations, in which the acceptance of the dominant ${g}\xspace {g}\xspace \to {H}\xspace\xspace$ contribution is modelled by Powheg+JHUGen+pythia, and Powheg MiNLO HJ+pythia generators, as discussed in Section \ref{['sec:DatasetsSimulationPAS']}, are shown in blue and brown, respectively. The sub-dominant component of the signal XH is indicated separately in green. In all estimations the total cross section is normalized to the SM estimate computed at NNLL+NNLO accuracy. Systematic uncertainties correspond to the accuracy of the generators used to derive the differential estimations. The bottom panel shows the ratio of data or theoretical estimates to the Powheg MiNLO HJ theoretical estimations.