Hadroproduction of t anti-t pair with a b anti-b pair with PowHel

TL;DR

The paper presents a PowHel-based simulation of pp → t t̄ b b̄ at 14 TeV to generate LHE events for NLO+PS predictions and precise background modeling of ttH analyses. It details the integration of the POWHEG-Box with HELAC-NLO, generation-cuts and suppression to optimize event generation, and numerical-precision techniques to stabilize loop amplitudes, including a fake-virtual reweighting scheme. The authors demonstrate consistency with existing NLO results and provide LHEs whose shapes match NLO predictions while offering a usable normalization for subsequent showering. The work delivers ready-to-use LHEs and methodological guidance to improve hadron-level predictions for ttH background studies in high-energy collisions.

Abstract

We simulate the hadroproduction of a top-antitop pair in association with a bottom-antibottom pair at 14 TeV LHC using the PowHel package. We use the generated events, stored according to the Les-Houches event format, to make predictions for differential distributions formally at the next-to-leading order (NLO) accuracy and we compare these to existing predictions accurate at NLO.

Figures (8)

• Figure 1: Dependence of the total cross section at LO and NLO accuracy, with cuts shown in the legend.
• Figure 2: (a) Transverse momentum distribution of the $b$-jet and (b) that of the $b\bar{b}$-jet pair at the LHC at $\sqrt{s} = 14$ TeV using PowHel. The shaded bands correspond to cross sections obtained with varying the scale around the default one in the range $[\mu_0/2,2 \mu_0]$. The lower panels show the NLO predictions normalized by the predictions at LO, with errorbars representing the statistical accuracy of the numerical integration.
• Figure 3: Same as Figure \ref{['fig:ptb-nlo']} for (a) the rapidity distribution and (b) invariant mass distribution of the $b\bar{b}$-jet pair.
• Figure 4: Distribution of weights before and after reweighting.
• Figure 5: Distribution of (a) transverse momentum (b) rapidity of the hardest $b$-jet at the LHC at $\sqrt{s} = 14$ TeV using PowHel. Distributions from LHE's are denoted LHE, while those at NLO accuracy by NLO. The shaded bands correspond to cross sections obtained with varying the scale around the default one in the range $[\mu_0/2,2 \mu_0]$. The lower panels show the NLO predictions normalized by the predictions from LHE's, with errorbars representing the combined statistical accuracy of the numerical integrations.