NNLO computational techniques: The cases and

Abstract

A large set of techniques needed to compute decay rates at the two-loop level are derived and systematized. The main emphasis of the paper is on the two Standard Model decays H → γγ and H → gg. The techniques, however, have a much wider range of application: they give practical examples of general rules for two-loop renormalization; they introduce simple recipes for handling internal unstable particles in two-loop processes; they illustrate simple procedures for the extraction of collinear logarithms from the amplitude. The latter is particularly relevant to show cancellations, e.g. cancellation of collinear divergencies. Furthermore, the paper deals with the proper treatment of non-enhanced two-loop QCD and electroweak contributions to different physical (pseudo-)observables, showing how they can be transformed in a way that allows for a stable numerical integration. Numerical results for the two-loop percentage corrections to H → γγ, gg are presented and discussed. When applied to the process pp → gg + X → H + X, the results show that the electroweak scaling factor for the cross section is between −4% and +6% in the range 100 GeV < M H < 500 GeV, without incongruent large effects around the physical electroweak thresholds, thereby showing that only a complete implementation of the computational scheme keeps two-loop corrections under control.

Observation of a new boson with mass near 125 GeV in pp collisions at $ \sqrt{s}=7 $ and 8 TeV

“…The calculations include NLO QCD and EW corrections, and all interference effects up to NLO [25,26,[89][90][91][92][93][94]. For all the other final states hdecay [91,92] is used, which includes NLO QCD and NLO EW corrections.…”

Higgs production at the lHC

“…[24] for the Tevatron: the starting point is the Fortran code HIGLU 4 [58, 59] which evaluates the gg → H cross section at exact NLO in QCD (i.e. with the exact contributions of the top and bottom quark loops) to which we add the NNLO QCD contribution in the infinite top-quark mass limit, but with the LO normalisation containing the exact m t and m b dependence; grids for the exact NLO electroweak and the mixed QCD-electroweak corrections are then implemented within the code (they have been added in the partial factorization scheme [49], see section 2.2.2). The production cross sections are shown at the lHC with √ s = 7 TeV in figure 1 for an updated value of the top quark mass and when the partonic cross section is folded with the latest NNLO MSTW2008 public set of PDFs [60].…”

Search for the Standard Model Higgs Boson in the Decay ChannelH→ZZ→4linppCollisions atsChatrchyan1, Khachatryan2, Sirunyan3 et al. 2012Phys. Rev. Lett.921100View full textAdd to dashboardCite

“…The total cross section is scaled by the branching fraction BðH ! 4'Þ calculated with PROPHECY4F which includes NLO QCD and electroweak corrections and all interference effects at NLO [24,[38][39][40][41], in particular, effects specific to the 4e and 4 channels. The SM background contribution from ZZ production via q " q is generated at NLO with POWHEG, while other diboson processes (WW, WZ) are generated with PYTHIA with cross sections rescaled to NLO predictions.…”