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Effective K-factors for gg -> H -> WW -> lnu lnu at the LHC

G. Davatz, G. Dissertori, M. Dittmar, M. Grazzini, F. Pauss

TL;DR

This paper tackles accurate modeling of the SM Higgs search channel gg→H→WW→lνlν at the LHC by embedding higher-order QCD corrections into a PYTHIA-based simulation through a pT-dependent reweighting. It defines and applies an effective experimental K-factor that aligns LO Monte Carlo spectra with NNLL+NNLO/Higgs and NLL+NLO/WW predictions, while accounting for jet veto effects. The study finds an effective K-factor for MH≈165 GeV around 2.04 and demonstrates enhanced discovery potential, with S/B around 1:2 to 2:1 and 5σ significance achievable at roughly 0.4 fb⁻¹. The reweighting framework offers a practical path to incorporate higher-order corrections in other channels with similar jet activity characteristics.

Abstract

A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg -> H -> WW -> lnu lnu, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb^{-1}. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15 % smaller than the theoretical inclusive K-factor.

Effective K-factors for gg -> H -> WW -> lnu lnu at the LHC

TL;DR

This paper tackles accurate modeling of the SM Higgs search channel gg→H→WW→lνlν at the LHC by embedding higher-order QCD corrections into a PYTHIA-based simulation through a pT-dependent reweighting. It defines and applies an effective experimental K-factor that aligns LO Monte Carlo spectra with NNLL+NNLO/Higgs and NLL+NLO/WW predictions, while accounting for jet veto effects. The study finds an effective K-factor for MH≈165 GeV around 2.04 and demonstrates enhanced discovery potential, with S/B around 1:2 to 2:1 and 5σ significance achievable at roughly 0.4 fb⁻¹. The reweighting framework offers a practical path to incorporate higher-order corrections in other channels with similar jet activity characteristics.

Abstract

A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg -> H -> WW -> lnu lnu, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb^{-1}. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15 % smaller than the theoretical inclusive K-factor.

Paper Structure

This paper contains 6 sections, 3 equations, 7 figures, 4 tables.

Table of Contents

  1. Introduction
  2. $K$-factors and the reweighting technique
  3. Higgs signal selection
  4. Signal and background _T $p_\mathrm{T}$ spectra
  5. Results
  6. Summary

Figures (7)

  • Figure 1: Number of accepted signal and background events as a function of the _T^jet $p_\mathrm{T}^\mathrm{jet}$ of the leading jet. The simulated Higgs mass is 165 GeV. All cuts except the jet veto are applied. Events without a reconstructed jet are evenly distributed over the first 10 bins, since only those jets are counted which have a reconstructed _T^jet $p_\mathrm{T}^\mathrm{jet}$ larger than 20 GeV.
  • Figure 2: Signal selection efficiency as a function of the Higgs transverse momentum, for a Higgs mass of 165 GeV and three different jet veto cuts. For completeness, the efficiency curve for all cuts, excluding the jet veto, is also shown.
  • Figure 3: The Higgs production cross section for $\rm{gg}\rightarrow\rm{H}$, as a function of the Higgs transverse momentum _T^H $p_\mathrm{T}^\mathrm{H}$, for a Higgs mass of 165 GeV, obtained with PYTHIA and with the NNLL+NNLO calculation. The spectrum from PYTHIA rescaled with the inclusive $K$-factor is also shown for comparison.
  • Figure 4: The _T^H $p_\mathrm{T}^\mathrm{H}$ dependence of the $K$-factor, as defined in Section \ref{['defKfacs']}.
  • Figure 5: The _T $p_\mathrm{T}$ spectrum of the non-resonant WW system with a mass of $170\pm 5$ GeV, obtained from PYTHIA and from the NLL+NLO calculation. The spectrum from PYTHIA rescaled with the inclusive $K$-factor is also shown for comparison.
  • ...and 2 more figures