Production-decay interferences at NLO in QCD for t-channel single-top production

TL;DR

This work develops a gauge-invariant, effective-theory framework to include production–decay interference effects in $t$-channel single-top production at NLO in QCD by expanding in the top off-shellness $\Delta_t/m_t$ and the couplings $\alpha_s$, $\alpha_{ew}$. By separating hard (factorizable) and soft (non-factorizable) contributions via the method of regions and resumming finite-width effects through the complex pole $\mu_t^2=m_t^2-i m_t\Gamma_t$, the authors compute both virtual and real corrections consistently beyond the narrow-width approximation. They present explicit helicity amplitudes for tree level and loop/corrected contributions, implement two IR-subtraction schemes, and validate the approach by comparing three levels of approximation against established results. Numerically, inclusive cross sections show small corrections from non-factorizable effects, while differential distributions exhibit observable-dependent off-shell impacts, particularly near resonance edges and under realistic cuts. The method's generality suggests applicability to other resonant processes, including top-quark pair production, offering a practical tool for precise top-quark property measurements at the LHC.

Abstract

We present a calculation of O(α_s) contributions to the process of t-channel single-top production and decay, which include virtual and real corrections arising from interference of the production and decay subprocesses. The calculation is organized as a simultaneous expansion of the matrix elements in the couplings α_{ew},α_s and the virtuality of the intermediate top quark, (p_t^2-m_t^2)/m_t^2 ~ Γ_t/m_t, and extends earlier results beyond the narrow-width approximation.

Figures (6)

• Figure 1: Tree-level Feynman diagrams for the process $q b \rightarrow q' b W$. The figure shows both purely EW contributions, diagrams (a) and (c), and mixed QCD-EW contributions, diagrams (b). The semileptonic (on-shell) decay of the $W$ is understood.
• Figure 2: Virtual QCD corrections to t-channel single-top production at leading order in $\Delta_t/m_t$.
• Figure 3: Real QCD corrections to resonant t-channel single-top production at leading order in $\Delta_t/m_t$.
• Figure 4: Transverse top mass distribution for on-shell (dashed lines) and resonant (solid lines) top-quark production. LO results are shown in red, pNLO results (see text for explanation) in green and full NLO results in red. The orange line shows the subleading QCD contribution.
• Figure 5: $H_T({\rm had})$ distribution for on-shell (dashed) and resonant (solid) top-quark production at LO (blue) and NLO (red). The orange line shows the subleading QCD contribution.