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Register a new userHadronic decays of Higgs boson at NNLO matched with parton shower
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We present predictions for hadronic decays of the Higgs boson at next-to-next-to-leading order (NNLO) in QCD matched with parton shower based on the POWHEG framework. Those include decays into bottom quarks with full bottom-quark mass dependence, light quarks, and gluons in the heavy top quark effective theory. Our calculations describe exclusive decays of the Higgs boson with leading logarithmic accuracy in the Sudakov region and next-to-leading order (NLO) accuracy matched with parton shower in the three-jet region, with normalizations fixed to the partial width at NNLO. We estimated remaining perturbative uncertainties taking typical event shape variables as an example and demonstrated the need of future improvements on both parton shower and matrix element calculations. The calculations can be used immediately in evaluations of the physics performances of detector designs for future Higgs factories.
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We present results for Higgs boson pair production with variations of the trilinear Higgs boson self-coupling at next-to-leading order (NLO) in QCD including the full top quark mass dependence. Differential results at 14 TeV are presented, and we discuss the implications of anomalous trilinear couplings as well as differences between the PYTHIA 8.2 and HERWIG 7.1 parton showers in combination with POWHEG. The implementation of the NLO QCD calculation with variable Higgs boson self-coupling is made publicly available in the POWHEG-BOX-V2 Monte Carlo framework. A simple method for using the new implementation to study also variations of the top quark Yukawa coupling is described.
We present a new set of parton distributions obtained at NNLO. These differ from the previous sets available at NNLO due to improvements in the theoretical treatment. In particular we include a full treatment of heavy flavours in the region near the quark mass. In this way, an essentially complete set of NNLO partons is presented for the first time. The improved treatment leads to a significant change in the gluon and heavy quark distributions, and a larger value of the QCD coupling at NNLO, alpha_S(M_Z^2) = 0.1191 +/- 0.002(expt.) +/- 0.003(theory). Indirectly this also leads to a change in the light partons at small x and modifications of our predictions for W and Z production at the LHC. As well as the best-fit set of partons, we also provide 30 additional sets representing the uncertainties of the partons obtained using the Hessian approach.
We present the first combination of NLO QCD matrix elements for di-Higgs production, retaining the full top quark mass dependence, with a parton shower. Results are provided within both the POWHEG-BOX and MadGraph5_aMC@NLO Monte Carlo frameworks. We assess in detail the theoretical uncertainties and provide differential results. We find that, as expected, the shower effects are relatively large for observables like the transverse momentum of the Higgs boson pair, which are sensitive to extra radiation. However, these shower effects are still much smaller than the differences between the Born-improved HEFT approximation and the full NLO calculation in the tails of the distributions.
We present the Higgs Characterisation (HC) framework to study the properties of the Higgs boson observed at 125 GeV. In this report, we focus on CP properties of the top-quark Yukawa interaction, and show predictions at next-to-leading order accuracy in QCD, including parton-shower effects, for Higgs production in association with a single top quark at the LHC.
We derive the second-order QCD corrections to the production of a Higgs boson recoiling against a parton with finite transverse momentum, working in the effective field theory in which the top quark contributions are integrated out. To account for quark mass effects, we supplement the effective field theory result by the full quark mass dependence at leading order. Our calculation is fully differential in the final state kinematics and includes the decay of the Higgs boson to a photon pair. It allows one to make next-to-next-to- leading order (NNLO)-accurate theory predictions for Higgs-plus-jet final states and for the transverse momentum distribution of the Higgs boson, accounting for the experimental definition of the fiducial cross sections. The NNLO QCD corrections are found to be moderate and positive, they lead to a substantial reduction of the theory uncertainty on the predictions. We compare our results to 8 TeV LHC data from ATLAS and CMS. While the shape of the data is well-described for both experiments, we agree on the normalization only for CMS. By normalizing data and theory to the inclusive fiducial cross section for Higgs production, good agreement is found for both experiments, however at the expense of an increased theory uncertainty. We make predictions for Higgs production observables at the 13 TeV LHC, which are in good agreement with recent ATLAS data. At this energy, the leading order mass corrections to the effective field theory prediction become significant at large transverse momenta, and we discuss the resulting uncertainties on the predictions.
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