Applying the POWHEG method to top pair production and decays at the ILC

TL;DR

The paper develops and applies a POWHEG-based NLO+PS framework for top-quark pair production and semileptonic decays in e+e- collisions at the ILC, interfacing with Herwig++ and incorporating beam polarization and spin correlations. It formulates hardest-emission generation for both production and decay, uses undecayed-matrix-element bounding and decay-density matrices to handle spin effects, and implements a truncated shower before the hardest emission. Through comparisons of lepton spectra and bottom-quark kinematics, the study finds that POWHEG emissions slightly broaden LO distributions while decay radiation more effectively softens bottom-quark spectra, validating the approach for precision top-quark physics at the ILC. The work provides a practical, high-precision event-generation framework for future ILC analyses with realistic hadron-level predictions.

Abstract

We study the effects of gluon radiation in top pair production and their decays for e+e- annihilation at the ILC. To achieve this we apply the POWHEG method and interface our results to the Monte Carlo event generator Herwig++. We consider a center-of-mass energy of \sqrt{s}=500 GeV and compare decay correlations and bottom quark and anti-quark distributions before hadronization.

Figures (16)

• Figure 1: Transverse momentum, $k_T$.
• Figure 2: Phase space and $y$ solutions for $\kappa=0.01$ in the region $x>y$.
• Figure 3: Phase space and $y$ solutions for $\kappa=0.028$ in the region $x>y$.
• Figure 4: Phase space and distribution of hardest emissions for axial (left) and vector(right) currents with $\rho=0.1225$.
• Figure 5: Phase space and distribution of hardest emissions for an axial current with $\rho=0.0625$ (left) and $\rho=0.01361$ (right).