NLO Uncertainties in Higgs + 2 jets from Gluon Fusion

TL;DR

This paper analyzes the perturbative uncertainties in NLO predictions for Higgs production with two jets via gluon fusion, highlighting challenges in distinguishing it from vector boson fusion due to large uncertainties.

Contribution

It provides a detailed study of NLO perturbative uncertainties in Higgs + 2 jets from gluon fusion and evaluates the effectiveness of the ST method for uncertainty estimation.

Findings

VBF selection cuts can increase ggF contamination.

Perturbative uncertainties grow with restrictive cuts.

Careful cut choices are essential to distinguish production modes.

Abstract

A central ingredient in establishing the properties of the newly discovered Higgs-like boson is to isolate its production via vector boson fusion (VBF). With the typical experimental selection cuts, the VBF sample is contaminated by a 25% fraction from Higgs + 2 jet production via gluon fusion (ggF) which has large perturbative uncertainties. We perform a detailed study of the perturbative uncertainties in the NLO predictions for pp -> H+2 jets via ggF used by the ATLAS and CMS collaborations, with the VBF selection cuts of their current H -> gamma gamma analyses. We discuss in detail the application of the so-called "ST method" for estimating fixed-order perturbative uncertainties in this case, and also consider generalizations of it. Qualitatively, our results apply equally to other decay channels with similar VBF selection cuts. Typical VBF selections include indirect restrictions or explicit vetoes on additional jet activity, primarily to reduce non-Higgs backgrounds. We find that such restrictions have to be chosen carefully and are not necessarily beneficial for the purpose of distinguishing between the VBF and ggF production modes, since a modest reduction in the relative ggF contamination can be easily overwhelmed by its quickly increasing perturbative uncertainties.