Standard Model Higgs boson production in association with a top anti-top pair at NLO with parton showering

TL;DR

The paper develops and validates a framework to predict Standard Model Higgs production in association with a top-antitop pair at NLO accuracy matched to parton showers. By interfacing HELAC-NLO/Oneloop with the POWHEG-Box and connecting to PYTHIA or HERWIG, the authors generate hadron-level ttH events with decays, showering, and hadronization, and they perform thorough cross-checks against established results. Key contributions include consistent NLO+PS predictions, quantification of shower effects on observables, and detailed comparisons of shower programs, with results that support realistic simulations for Higgs searches and background studies. The work provides practical, publicly available event samples and sets the stage for further background analyses within the same framework, enhancing the precision and realism of collider predictions for ttH production.

Abstract

We present predictions for the production cross section of a Standard Model Higgs boson in association with a top-antitop pair at next-to-leading order accuracy using matrix elements obtained from the HELAC-Oneloop package. The NLO prediction was interfaced to the PYTHIA and HERWIG shower Monte Carlo programs with the help of POWHEG-Box, allowing for decays of massive particles, showering and hadronization, thus leading to final results at the hadron level.

Figures (9)

• Figure 1: Transverse momentum and rapidity distributions of the Higgs boson at the Tevatron from our calculation by means of POWHEG-HELAC (POWHEG) and from Ref. Beenakker:2002nc (pure NLO). The lower panels show the ratio of the results (POWHEG/NLO).
• Figure 2: Transverse momentum distribution of the hardest jet. The results at the decay level (dashed line) are compared to the ones at the SMC level (solid line), obtained by interfacing POWHEG-HELAC to PYTHIA . No selection cuts were applied.
• Figure 3: The same as Fig. \ref{['fig:pTj']}, as for the rapidity of the hardest jet.
• Figure 4: Invariant mass distribution of the two hardest lowest-lying B hadrons at the SMC level. These results are presented in sigma per bin, just to allow an easier comparison with the results of Ref. Hirschi:2011pa, having been obtained in the same setup, without applying any cut. The effects of including all H decay channels, with respect to the case of a single H $\rightarrow$ b$\bar{{\rm b}}$ channel (dashed line), were computed by interfacing POWHEG-HELAC to both PYTHIA (solid line) and HERWIG (dash-dotted line).
• Figure 5: The same as Fig. \ref{['fig:mbb']}, as for the azimuth-rapidity distance correlations of the two hardest lowest-lying B hadrons.