Resummation ambiguities in the Higgs transverse-momentum spectrum in the Standard Model and beyond

TL;DR

This paper investigates the ambiguities in matching fixed-order and all-order resummed calculations for the Higgs transverse momentum spectrum, comparing different algorithms and approaches to reduce discrepancies, especially at high pT.

Contribution

It provides a detailed comparison of matching scale algorithms and explores modifications to Monte Carlo methods to minimize ambiguities in Higgs pT predictions.

Findings

Matching ambiguities are significant at high pT.

Different resummation methods largely agree at low pT.

Modifications to Monte Carlo implementations can reduce discrepancies.

Abstract

We study the prediction for the Higgs transverse momentum distribution in gluon fusion and focus on the problem of matching fixed- and all-order perturbative results. The main sources of matching ambiguities on this distribution are investigated by means of a twofold comparison. On the one hand, we present a detailed qualitative and quantitative comparison of two recently introduced algorithms for determining the matching scale. On the other hand, we apply the results of both methods to three widely used approaches for the resummation of logarithmically enhanced contributions at small transverse momenta: the MC@NLO and POWHEG Monte Carlo approaches, and analytic resummation. While the three sets of results are largely compatible in the low-pT region, they exhibit sizable differences at large pT. We show that these differences can be significantly reduced by suitable modifications of formally subleading terms in the Monte Carlo implementations. We apply our study to the Standard Model Higgs boson and to the neutral Higgs bosons of the Two-Higgs-Doublet Model for representative scenarios of the parameter space, where the top- and bottom-quark diagrams enter the cross section at different strength.