Finite-width effects in the near-threshold ZZZ and ZWW production at ILC

TL;DR

This paper calculates the cross-sections for near-threshold off-shell ZZZ and ZWW production at the ILC, emphasizing the importance of finite width effects of unstable particles in Higgs boson searches.

Contribution

It introduces a method to incorporate finite-width effects of unstable particles in cross-section calculations near production thresholds.

Findings

Finite width effects are significant near the Higgs resonance.

Neglecting widths can lead to inaccurate cross-section estimates.

The method improves the precision of collider predictions.

Abstract

We calculate the cross-section of the near-threshold off-shell $ZZZ$ and $ZW^+W^-$ production at the International Linear Collider taking into account their instability and the principal part of NLO corrections. The calculations are performed in the framework of the model of unstable particles with smeared mass-shell. We show that the contribution of the finite $Z/W$ and $H$ widths (their instability) is large in the Higgs resonance range and should be taken into account in the Higgs boson searches at future colliders.