Higgs boson production in association with top quarks in the POWHEG BOX (1501.04498v1)

Abstract: We present results from the analytic calculation of top+antitop+Higgs hadronic production at Next-to-Leading Order in QCD interfaced with parton-shower Monte Carlo event generators in the POWHEG BOX framework. We consider kinematic distributions of the top quark and Higgs boson at the 8 TeV Large Hadron Collider and study the theoretical uncertainties due to specific choices of renormalization/factorization scales and parton-showering algorithms, namely PYTHIA and HERWIG. The importance of spin-correlations in the production and decay stages of a top/antitop quark is discussed on the example of kinematic distributions of leptons originating from the top/antitop decays. The corresponding code is now part of the public release of the POWHEG BOX.

• The paper demonstrates that NLO-QCD calculations within the POWHEG BOX framework reliably model ttH production with full spin-correlation effects.
• The analysis reveals that using dynamical scales can reduce theoretical uncertainties by over 10% in key kinematic regions.
• Interfacing POWHEG with parton showers like PYTHIA and HERWIG exposes minor discrepancies that are critical for refining Standard Model tests.

Overview of Higgs Boson Production with Top Quarks in the POWHEG BOX Framework

The paper presents a detailed paper of the Higgs boson production in association with top (t) and antitop ($\bar{t}$) quarks, an area of significant interest following the discovery of the Higgs boson at CERN's Large Hadron Collider (LHC). By examining this production mode at Next-to-Leading Order (NLO) in Quantum Chromodynamics (QCD) and interfacing it with parton-shower Monte Carlo event generators using the POWHEG BOX framework, this research advances the theoretical understanding of Higgs boson interactions with heavy quarks.

Theoretical and Computational Framework

The authors investigate $t\bar{t}H$ production at 8 TeV LHC energies, focusing on the impact of theoretical uncertainties related to the choice of renormalization/factorization scales and parton-shower algorithms. They employ the POWHEG BOX framework, a widely used tool for NLO calculations matched with parton showers, choosing PYTHIA and HERWIG as the interfacing parton-shower generators.

An essential aspect of the paper is the inclusion of spin correlations in the production and decay of top quarks, a factor often overlooked in simpler treatments. The complete code supporting these calculations is now integrated into the public release of the POWHEG BOX, facilitating broader use in the experimental community.

Numerical Results and Implications

The paper scrutinizes several kinematic distributions, such as the transverse momentum ($p_T$) and rapidity distributions of final-state particles. The results indicate notable differences between fixed and dynamical scale choices, with potential scale uncertainties exceeding 10% in certain phase-space regions. The paper exhibits that employing dynamical scales could slightly mitigate these uncertainties.

Interfacing the NLO-QCD results with PYTHIA and HERWIG results in minor discrepancies between the predictions, attributed largely to differing parton-shower implementations. Specifically, HERWIG tends to systematically enhance the low $p_T$ region compared to PYTHIA6, while PYTHIA8 generally aligns more closely with HERWIG's entire $p_T$ range.

Another striking outcome is the theoretical uncertainty from scale dependencies, which are non-negligible, emphasizing the necessity for careful choice and justification of scales in experimental analyses. Further, incorporating spin-correlation effects demonstrably alters predictions for angular correlations between leptonic decay products of top quarks, thereby strengthening the LHC's sensitivity in the $t\bar{t}H$ channel.

Broader Context and Future Directions

This investigation contributes significantly to refining the theoretical tools available for LHC analyses of $t\bar{t}H$ production. By improving the accuracy and reliability of simulations used to extract Higgs couplings from experimental data, the work supports precise tests of the Standard Model and aids in probing for potential new physics.

Looking forward, further development in methodologies to include higher-order corrections, especially concerning decay processes, could enhance the precision of theoretical predictions. Moreover, investigating the integration with other parton-shower generators and addressing omitted contributions (such as vetoed truncated showers in HERWIG) remain pertinent to reducing systematic theoretical uncertainties.

Ultimately, the advances detailed in this paper set the stage for more accurate data interpretations from current and future collider experiments, bolstering both theoretical and experimental high-energy physics research.