ATLAS document

Inclusive, differential and production mode cross sections of the Higgs boson production in proton-proton collisions are measured in the H → Z Z∗ → 4` decay channel. The proton−proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2017, corresponding to an integrated luminosity of 79.8 fb−1. The inclusive fiducial cross section for the process H → Z Z∗ → 4` is measured to be σfid = 4.04 ± 0.47 fb, while the Standard Model prediction is σfid,SM = 3.35 ± 0.15 fb. The cross-section times H → Z Z∗ branching ratio for gluon fusion and vector-boson fusion production are measured to be 1.22 ± 0.18 pb and 0.25 ± 0.09 pb, respectively. All measurements are in agreement with the Standard Model prediction.


Introduction and methods
This note presents measurements of the total Higgs boson production cross section and of the differential cross section as a function of Higgs boson transverse momentum p T,H using the H → γγ and H → Z Z * → 4 (where = e, µ throughout this note) final states. The results are obtained from the full Run-2 13 TeV proton-proton dataset, produced at the Large Hadron Collider (LHC), recorded by the ATLAS detector [1], and corresponding to an integrated luminosity of 139.0±2.4 fb −1 [2, 3]. The measurements are extrapolated to the full phase space and the measured cross sections are compared to Standard Model (SM) predictions.
Full descriptions of the measurement of the event yields in the H → γγ and H → Z Z * → 4 decay channels are given in Refs. [12,13]. Corrections are applied to these yields accounting for luminosity, detector effects, fiducial acceptances, and branching fractions. The SM values of the Higgs boson branching fractions are used, and the acceptances are based on SM predictions. Uncertainties due to the model dependence of the acceptance factors are evaluated by varying the contribution of the different Higgs boson production modes. The value of the Higgs boson mass is assumed to be 125.09 GeV [14]. The combined differential cross-section measurement reported here is based on results obtained in the individual channels using bin-by-bin correction factors.

Process Accuracy
Fraction [%] ggF N 3 LO in QCD, NLO in EW 87.2 VBF (approximate) NNLO in QCD, NLO in EW 6.8 VH qq/qg: NNLO in QCD, NLO in EW; gg: NLO+NLL in QCD 4.0 ttH + tH ttH: NLO in QCD, NLO in EW, tH: NLO in QCD 1.1 bbH NNLO (NLO) in QCD for 5FS (4FS) 0.9 The branching fraction for a Higgs boson with mass m H = 125.09 GeV decaying to H → γγ is predicted to be (0.227 ± 0.007)% [28], and the branching ratio to the four-lepton final state is predicted to be (0.0125 ± 0.0003)% [28]. Both branching ratios are calculated with HDECAY [62,63] and PROPHECY4F [64,65] and include the complete NLO QCD and EW corrections. In the H → Z Z * → 4 case, the interference effects between identical final-state fermions are included.
A likelihood combination of the two decay channels is performed, following the method described in Ref.
[4]. The p T,H binning in the H → γγ analysis is finer than that in the H → Z Z * → 4 analysis. Where needed, the sum of the respective H → γγ bins is combined with one H → Z Z * → 4 bin. Experimental and theoretical uncertainties that affect both channels are correlated by the implementation of common nuisance parameters. These include the uncertainties in the integrated luminosity, in the Higgs boson mass value, in the description of the pileup in the simulation, and in the contributions of the different Higgs boson production modes. Additionally, the uncertainties in the branching fractions are correlated through the correlation of the corresponding underlying sources. Finally, the uncertainties in the acceptance and correction factors due to variations of the modeling of the parton shower are also correlated. All other uncertainties are treated as uncorrelated. The asymptotic approximation [66] is used when computing the uncertainties in the cross-section measurements. The validity of this approximation has been verified in previous analyses by performing pseudo-experiments.

Results and Conclusion
The ) is obtained. All three results are in agreement with the SM prediction of 55.6 ± 2.5 pb. Figure 1 shows the measured total cross section, together with the cross sections measured at √ s = 7 and 8 TeV [67].
The differential cross sections as a function of p T,H for the individual channels and their combination are shown in Figure 2, along with the SM prediction described above. The uncertainty band on the SM prediction includes PDF and α S uncertainties as well as those due to missing higher-order corrections, obtained following the method described in Ref.
[6]. The measurement uncertainty is dominated by the statistical component. The background modeling uncertainty in the H → γγ analysis is the main source of systematic uncertainty, followed by the luminosity estimate.
The measurements in the two decay channels are found to be compatible with a p-value of 76% for the total cross section and 11% for the p T,H distribution. The combined measurements are compatible with the SM predictions with a p-value of 96% for the total cross section and 78% for the p T,H distribution. Both compatibility checks are performed using a likelihood approach, neglecting the uncertainties in the SM prediction. The grey bands on the combined measurements represent the systematic uncertainty, while the error bars show the total uncertainty. The light blue band shows the estimated uncertainty due to missing higher-order corrections, and the dark blue band indicates the total uncertainty. The total theoretical uncertainty corresponds to the higher-order-correction uncertainty summed in quadrature with the sum of the PDF and α S uncertainties, and is partially correlated across values of the center-of-mass energy.