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

TL;DR

Problem: provide precise QCD predictions for associated WH production with H→bb under realistic LHC selection cuts, including higher-order radiative corrections in both production and decay. Approach: compute NNLO QCD for $pp\to WH$ with $H\to bb$ at NLO, using the narrow-width approximation and differential observables, and compare fixed-order results to MC@NLO across 8 and 14 TeV. Key findings: NNLO production reduces the cross section depending on cuts but has a mild effect on the Higgs $p_T$ spectrum; NLO corrections to $H\to bb$ are important for spectra yet largely captured by parton showers, and jet vetoes introduce perturbative instabilities; in 14 TeV boosted analyses the $p_T$ shape remains stable while normalizations carry larger uncertainties. Significance: provides more reliable predictions for WH Higgs studies and informs MC validation and potential future NNLO+PS implementations.

Abstract

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.

Figures (7)

• Figure 1: Left panel: Transverse-momentum distribution of the $b$-jets pair computed at NLO with LO decay (red dot-dashes), NLO with NLO decay (blue solid), NNLO with NLO decay (cyan dashes) and with MC@NLO (magenta dots). Right panel: The same distributions normalized to the full NLO result. The NLO, NNLO and MC@NLO uncertainty bands are also shown. No cuts except the $b$-jet selection are applied.
• Figure 2: As in Fig. \ref{['fig:nocuts']} but when selection cuts are applied. The inset plot shows the region around $p_T^{bb}\sim 160$ GeV.
• Figure 3: As in Fig. \ref{['fig:cuts']} but with an additional veto on light jets.
• Figure 4: Comparison of NLO with NLO decay (blue solid), MC@NLO with default scale (magenta dots), MC@NLO with fixed scale (green dot-dashes), MC@NLO without hadronization (black dashes). Left panel: without jet veto. Right panel: with jet veto.
• Figure 5: Invariant mass distribution of the pair of $b$-jets computed at NLO with LO decay (red dot-dashes), NLO with NLO decay (blue solid), NNLO with NLO decay (cyan dashes), MC@NLO without hadronization (black dots) and with default MC@NLO (magenta dots). The applied cuts are described in the text. Left panel: without jet veto. Right panel: with jet veto.