NLO tools and the background to $H\rightarrow WW$

TL;DR

This paper investigates how different NLO matrix element and parton shower merging methods affect the estimation of the $WW$ background in $H\rightarrow WW$ searches at the LHC, highlighting potential underestimations in background size and uncertainty.

Contribution

It compares various NLO merging implementations to assess their impact on background shape and size in Higgs to WW analyses.

Findings

Background estimates may be underestimated.

Uncertainty in background modeling could be larger than previously thought.

Different NLO merging methods produce varying background predictions.

Abstract

A theory input is needed for the estimation of the largest background for the $H\rightarrow WW$ search at the LHC. This is the shape of the $m_{\ell\ell}$ spectrum from continuum $WW$ production. We find this to depend on how NLO matrix elements are merged with parton showers, and we compare the results from a number of different implementations. The results suggest that both the size of the background estimate and its uncertainty may have been underestimated. This conclusion is reinforced by a "Note Added", which comments on the LHC results released on November 14 2012.