NLO electroweak corrections to off-shell top-antitop production with leptonic decays at the LHC

TL;DR

The study provides the first full NLO EW corrections to off-shell top-quark pair production with leptonic decays at the LHC, including all off-shell, non-resonant, and interference effects. It demonstrates that integrated EW effects are small ($<1\%$) but become substantial in high-$p_T$ tails ($\sim$few-$10\%$), with photon-induced contributions partially offsetting the negative Sudakov corrections in some observables. Two double-pole approximations (WW and tt) are explored, showing the WW DPA closely reproduces the full result across most distributions, while the tt DPA can fail in high-energy regions, highlighting the importance of full off-shell treatment. The work validates a sophisticated computational setup (MoCaNLO, Recola, Collier) and provides precise SM background predictions for top-quark-related measurements and new-physics searches at $13$ TeV.

Abstract

For the first time the next-to-leading-order electroweak corrections to the full off-shell production of two top quarks that decay leptonically are presented. This calculation includes all off-shell, non-resonant, and interference effects for the 6-particle phase space. While the electroweak corrections are below one per cent for the integrated cross section, they reach up to 15% in the high-transverse-momentum region of distributions. To support the results of the complete one-loop calculation, we have in addition evaluated the electroweak corrections in two different pole approximations, one requiring two on-shell top quarks and one featuring two on-shell W bosons. While the former deviates by up to 10% from the full calculation for certain distributions, the latter provides a very good description for most observables. The increased centre-of-mass energy of the LHC makes the inclusion of electroweak corrections extremely relevant as they are particularly large in the Sudakov regime where new physics is expected to be probed.

Figures (10)

• Figure 1: Representative tree-level Feynman diagrams with two (left), one (middle) and no (right) top-quark resonances.
• Figure 2: Representative real Feynman diagrams squared which feature interference between QCD and EW tree-level diagrams. Only the top quarks are represented as the inclusion of their decay products does not alter the discussion.
• Figure 3: Representative one-loop Feynman diagrams squared. The diagram on the left-hand side represents an EW correction to the QCD process. It can also be interpreted as a QCD correction to the EW amplitude interfered with the QCD amplitude. The right-hand side shows a QCD correction to the QCD amplitude interfered with the EW amplitude. Only the top quarks are represented as the inclusion of their decay products does not alter the discussion.
• Figure 4: Representative octagon and heptagon one-loop Feynman diagrams.
• Figure 5: Schematic representation of the two DPAs. On the left-hand side the two W bosons are projected on shell, while on the right-hand side the two top quarks are projected on shell.