arXiv subjects

Massimiliano Grazzini

Publications and source records attributed to Massimiliano Grazzini.

60 records · Page 4Linked to original sources

arXiv2015

Wgamma and Zgamma production at the LHC in NNLO QCD

We consider the production of $Wγ$ and $Zγ$ pairs at hadron colliders. We report on the complete fully differential computation of radiative corrections at next-to-next-to-leading order (NNLO) in QCD perturbation theory. The calculation includes the leptonic decay of the vector boson with the corresponding spin correlations, off shell effects and final-state photon radiation. We present numerical results for $pp$ collisions at 7 and 8 TeV and we compare them with available LHC data. In the case of $Zγ$ production, the impact of NNLO corrections is generally moderate, ranging from 8% to 18%, depending on the applied cuts. In the case of $Wγ$ production, the NNLO effects are more important, and range from 19% to 26%, thereby improving the agreement of the theoretical predictions with the data. As expected, the impact of QCD radiative corrections is significantly reduced when a jet veto is applied.

hep-ph↗

arXiv2014

Resummation of the transverse-energy distribution in Higgs boson production at the Large Hadron Collider

We compute the resummed hadronic transverse-energy ($E_T$) distribution due to initial-state QCD radiation in the production of a Standard Model Higgs boson of mass 126 GeV by gluon fusion at the Large Hadron Collider, with matching to next-to-leading order calculations at large $E_T$. Effects of hadronization, underlying event and limited detector acceptance are estimated using aMC@NLO with the Herwig++ and Pythia 8 event generators.

hep-ph↗

arXiv2014

Associated ZH production at hadron colliders: the fully differential NNLO QCD calculation

We consider Standard Model Higgs boson production in association with a Z boson in hadron collisions. We present a fully exclusive computation of QCD radiative corrections up to next-to-next-to-leading order (NNLO). Our calculation includes the Higgs boson decay to bottom quarks (b) in next-to-leading order QCD and the leptonic decay of the Z boson with finite-width effects and spin correlations. The computation is implemented in a parton level Monte Carlo program that makes possible to consider arbitrary kinematical cuts on the final-state leptons, the b jets and the associated QCD radiation, and to compute the corresponding distributions in the form of bin histograms. We assess the impact of QCD radiative effects in the boosted kinematics at the LHC and show that the inclusion of the NNLO corrections is crucial to control the pT spectrum of the Higgs boson candidate.

hep-ph↗

arXiv2014

Higher-order QCD effects for associated WH production and decay at the LHC

We consider Standard Model Higgs boson production in association with a W boson in hadron collisions. We supplement the fully exclusive perturbative computation of QCD radiative effects up to next-to-next-to-leading order (NNLO) with the computation of the decay of the Higgs boson into a bb pair at next-to-leading order (NLO). We consider the selection cuts that are typically applied in the LHC experimental analysis, and we compare our fixed-order predictions with the results obtained with the MC@NLO event generator. We find that NLO corrections to the H -> bb decay can be important to obtain a reliable pT spectrum of the Higgs boson, but that, in the cases of interest, their effect is well accounted for by the parton shower Monte Carlo. NNLO corrections to the production process typically decrease the cross section by an amount which depends on the detail of the applied cuts, but they have a mild effect on the shape of the Higgs pT spectrum. We also discuss the effect of QCD radiative corrections on the invariant mass distribution of the Higgs candidate.

hep-ph↗

arXiv2009

Perturbative QCD effects and the search for a H->WW->l nu l nu signal at the Tevatron

The Tevatron experiments have recently excluded a Standard Model Higgs boson in the mass range 160 - 170 GeV at the 95% confidence level. This result is based on sophisticated analyses designed to maximize the ratio of signal and background cross-sections. In this paper we study the production of a Higgs boson of mass 160 GeV in the gg -> H -> WW -> l nu l nu channel. We choose a set of cuts like those adopted in the experimental analysis and compare kinematical distributions of the final state leptons computed in NNLO QCD to lower-order calculations and to those obtained with the event generators PYTHIA, HERWIG and MC@NLO. We also show that the distribution of the output from an Artificial Neural Network obtained with the different tools does not show significant differences. However, the final acceptance computed with PYTHIA is smaller than those obtained at NNLO and with HERWIG and MC@NLO. We also investigate the impact of the underlying event and hadronization on our results.

hep-ph↗

arXiv2008

Higher-order QCD effects in the Higgs to ZZ search channel at the LHC

We present a consistent analysis of the signal as well as the irreducible background for the search of the SM Higgs boson in the ZZ decay channel at the LHC. Soft-gluons effects are resummed up to next-to-leading logarithmic accuracy, and the results are compared to those obtained with fixed order calculations and the MC@NLO event generator. The soft-gluon effects are typically modest but should be taken into account when precise predictions are demanded. Our results show that the signal over background ratio can be significantly enhanced with a cut on the transverse momentum pt(ZZ) of the ZZ pair. We also introduce a fully transverse angular variable that could give information about the CP nature of the Higgs boson.

hep-ph↗