NLO QCD corrections to t anti-t H production in hadron collisions

TL;DR

The paper delivers a comprehensive next-to-leading order QCD calculation for ttH production in hadron collisions, addressing both virtual (including complex pentagon diagrams) and real emission contributions. It introduces a robust framework combining universal pentagon reduction, mass-aware dipole subtraction, and cross-checks with phase-space slicing, yielding stabilized cross sections and final-state distributions. The results show K factors near 0.8 at the Tevatron and 1.2 at the LHC at the central scale, with significantly reduced scale dependence and reliable differential distributions, enhancing precision in top-Higgs coupling studies. The work also analyzes threshold effects (Sommerfeld corrections and soft-gluon logarithms) and assesses PDF uncertainties, providing a solid theoretical baseline for Higgs searches in ttH channels at current and future hadron colliders.

Abstract

The Higgs boson H of the Standard Model can be searched for in the channels p pbar / pp -> t tbar H + X at the Tevatron and the LHC. The cross sections for these processes and the final-state distributions of the Higgs boson and top quarks are presented at next-to-leading order QCD. To calculate these QCD corrections, a special calculational technique for pentagon diagrams has been developed and the dipole subtraction formalism has been adopted for massive particles. The impact of the corrections on the total cross sections is characterized by K factors, the ratios of the cross sections in next-to-leading order over leading order QCD. At the central scale mu_0 = (2 m_t + M_H)/2 the K factors are found to be slightly below unity for the Tevatron (K \sim 0.8) and slightly above unity for the LHC (K \sim 1.2). Including the corrections significantly stabilizes the theoretical predictions for total cross sections and for the distributions in rapidity and transverse momentum of the Higgs boson and top quarks.

Figures (19)

• Figure 1: The basic LO diagrams for the partonic processes $q\bar{q}, gg\to t\bar{t}H$.
• Figure 2: Representative diagrams of the gauge-invariant subsets (i)-(iii) of one-loop QCD diagrams, as described in the text.
• Figure 3: Generic set of Feynman diagrams contributing to real gluon emission and gluon-(anti)quark scattering.
• Figure 4: Generic diagram leading to the Coulomb singularity
• Figure 5: The scaling functions $f_{ab}$ for the partonic processes $ab \to t\bar{t}H$ as a function of $\eta = \hat{s}/4\mu_0^2 - 1$. The notation follows Eq. (\ref{['eq:scaling_fcts']}). The inserts show the ratio of the analytic threshold approximation and the complete numerical calculation. The Higgs-boson mass has been set to _$H$$M_H$H$$ = 120 GeV.