NNLO QCD corrections for pp → ℓ±ν̄ b ℓ′∓ν b̄ (fully off‑shell dileptonic tt̄)

Derive the next-to-next-to-leading order (NNLO) QCD corrections to the fully off-shell six-body process pp → ℓ±ν̄ b ℓ′∓ν b̄, so that these corrections can be used for kinematic reweighting of the POWHEG bb4 Monte Carlo simulations and thereby reduce modelling uncertainties in LHC measurements of dileptonic top-quark production.

Background

Precise modeling of dileptonic top-quark production requires treating the full pp → ℓ±ν̄ b ℓ′∓ν b̄ final state, including off-shell effects and interference between doubly resonant tt̄ and singly resonant tWb topologies. The POWHEG bb4 generator implements this process at NLO QCD, matched to parton showers, providing an improved description over traditional on-shell tt̄ simulations.

To further improve agreement with data and reduce systematic uncertainties, higher-order corrections are needed. The paper explicitly notes that NNLO QCD corrections to pp → ℓ±ν̄ b ℓ′∓ν b̄ are currently unknown, and that their availability would enable kinematic reweighting of POWHEG bb4 samples, analogous to practices used with on-shell tt̄ generators.

References

It is worth noting that NNLO QCD corrections to the $pp\to \ell\pm\bar{\nu}b\ell{'\mp}\nu\bar{b}$ are currently unknown, but active progress is being made on the theory side, such that it is reasonable to expect that approximate NNLO QCD corrections could be available within the next couple of years, allowing for kinematic reweighting of the bb4 MC simulations.

— ATLAS and CMS measurements of the $t\bar{t}$ cross section, including off-shell and near threshold  (2604.01984 - Ravina, 2 Apr 2026) in Subsection 3.1, Resonant and non-resonant production processes