Soft-gluon effects in WW production at hadron colliders

TL;DR

The paper addresses the need for accurate predictions of WW production at hadron colliders in the presence of soft-gluon emissions that dominate the small-$p_T^{WW}$ region. It implements $b$-space transverse-momentum resummation matched to NLO, achieving (almost) NNLL+LO accuracy and explicitly analyzes the impact on the $p_T^{WW}$ spectrum and leptonic observables. The results show that resummation effects are generally mild but can be enhanced by tight selection cuts, and that the resummed predictions are in good agreement with MC@NLO for a broad set of observables. This work improves the reliability of SM predictions for WW production, which is important for precision tests and for modeling backgrounds in Higgs and new-physics searches.

Abstract

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator.

Figures (8)

• Figure 1: Left: comparison of the transverse momentum spectra of the $WW$ pair obtained at NLL+LO, NNLL+LO and with MC@NLO. No cuts are applied. Right: NNLL+LO and MC@NLO results normalized to NLL+LO.
• Figure 2: NLL+LO spectra for different values of the resummation scale $Q$.
• Figure 3: Distributions in $p^l_{T{\rm min}}$ and $p^l_{T{\rm max}}$. No cuts are applied.
• Figure 4: Distributions in $p^l_{T{\rm min}}$ and $p^l_{T{\rm max}}$. Cuts A are applied.
• Figure 5: The $\Delta\phi$ distribution when cuts A are applied. The upper part of the plot shows the NLL+LO and MC@NLO results normalized to the NLO one.