Attached to the TWiki page, there is a file holding the correction factors to scale LO predictions for purely gluon-induced ZZ->2l2l' continuum production, off-shell SM Higgs production and their interference to NLO QCD accuracy. The k-factors are differential in the invariant mass of the ZZ system.

Phasespace definition and generator settings for the k-factor computation

  • PDF set: CT10nnlo
  • central scale: m(ZZ)/2 [variations m(ZZ) and m(ZZ)/4]
  • lepton selection cuts: pt(lepton) > 5 GeV, |eta(lepton)|<3

Details of the calculation

The calculation was performed by Raoul Roentsch (arXiv:1605.04610). Below the 2*m(top) threshold, massless quarks are fully considered while the top contribution is calculated the 1/m(top) expansion. Above the threshold, only massless quarks are taken into account in the k-factor calculation. The scale factors calculated for the SM Higgs boson (also entering in the interference computation) do always fully incorporate the top quark mass. Additional details on the calculation and assumptions entering in it can be found in this talk

Calculated k-factors

The rootfile HOQCD_KFactors_gg_ZZ.root contains the computed k-factors and the corresponding QCD scale uncertainties for the gg->H->ZZ signal, gg->ZZ background and for the interference

The content of the root file is the following:

  • gg_ZZ_[int/bkg/sig] correspond to the central value k factor for the signal, background, interference.
  • gg_ZZ_[int/bkg/sig]_[up/down] correspond to k factor for the up/down QCD scale variations k factor for the signal, background, interference.

Smooth version of the k-factors


These k-factors can be used on top of LO predictions to NLO QCD accuracy. Since the off-signal is known up NNLO QCD accuracy (see here) , an additional factor (corresponding to the NNLO/NLO off-shell signal k-factor) can be applied to all the three components. While doing so, NLO QCD scale uncertainties should be considered.

-- RobertoDiNardo - 2018-03-16

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Topic revision: r3 - 2018-03-19 - RobertoDiNardo
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