Full off-shell $t\bar{t}$ production in the semileptonic channel at the LHC

TL;DR

Full off-shell $t\bar{t}$ production in the $\ell+j$ channel requires finite-width, resonant/non-resonant, and interference effects for precision LHC predictions; this work provides a complete NLO calculation including both QCD and EW corrections to all Born amplitudes with IR-safe photon/jet treatment via fragmentation and conversion functions. It outlines the perturbative structure (LO: $\mathcal{O}(\alpha_s^4\alpha^2)$ to $\mathcal{O}(\alpha^6)$; NLO: $\mathcal{O}(\alpha_s^5\alpha^2)$ to $\mathcal{O}(\alpha^7)$) and uses a resonance window $|M_{jj}-m_W|<\mathcal{Q}_{\text{cut}}$ with ${\mathcal Q}_{\text{cut}}=20$ GeV to define the fiducial region. The results show that integrated cross sections are dominated by the resonant Born term with subleading NLO corrections generally at the percent level, while differential distributions in the high-$p_T$ tails exhibit corrections up to about 10% due to non-resonant and EW effects, highlighting the need for complete NLO for precision LHC phenomenology. The work provides IR-safe, complete predictions essential for LHC precision phenomenology, including HL-LHC, and informs background modeling for searches of new physics.

Abstract

In this contribution, we summarize our results on the complete NLO predictions for the production of off-shell top quark pairs in the $\ell+j$ channel at the LHC. All NLO QCD and electroweak corrections are consistently included across the full set of LO contributions and partonic subprocesses, while retaining finite-width effects of the top quarks and the electroweak gauge bosons. Resonant and non-resonant contributions as well as interference effects are included in the complete calculation. We pay special attention to infrared singularities associated with photons and jets appearing simultaneously in the final state. Fiducial integrated and differential cross-section results are presented for $pp$ collisions at $\sqrt{s}=13.6$ TeV.

Figures (2)

• Figure 1: Diagrammatic overview of the LO contributions and their corresponding NLO corrections for $pp \to \ell^- \bar{\nu}_\ell\, j_b j_b\, jj + X$.
• Figure 2: Differential distributions for $p_{T,b_1}$ (left) and $M_{b_1b_2}$ (right) at LO, $\mathrm{NLO}_{\mathrm{QCD}}$, and complete NLO, shown with ratio panels.