Top Quark Pair Production in Association with a Jet with NLO QCD Off-Shell Effects at the Large Hadron Collider

TL;DR

This calculation constitutes the first fully realistic NLO computation for top quark pair production with a final state jet in hadronic collisions and reduces the unphysical scale dependence by more than a factor of 3 and lower the total rate by about 13% compared to leading-order QCD predictions.

Abstract

We present a complete description of top quark pair production in association with a jet in the dilepton channel. Our calculation is accurate to next-to-leading order in QCD (NLO) and includes all non-resonant diagrams, interferences and off-shell effects of the top quark. Moreover, non-resonant and off-shell effects due to the finite W gauge boson width are taken into account. This calculation constitutes the first fully realistic NLO computation for top quark pair production with a final state jet in hadronic collisions. Numerical results for differential distributions as well as total cross sections are presented for the Large Hadron Collider (LHC) at 8 TeV. With our inclusive cuts, NLO predictions reduce the unphysical scale dependence by more than a factor of 3 and lower the total rate by about 13% compared to leading order QCD (LO) predictions. In addition, the size of the top quark off-shell effects is estimated to be below 2%.

Figures (3)

• Figure 1: Representative Feynman diagrams, involving two (first diagram), one (second diagram) and no top quark resonances (third diagram), contributing to the leading order $pp \to e^+\nu_e \mu^- \bar{\nu}_\mu b\bar{b}j$ process at ${\cal O}(\alpha_s^3 \alpha^4)$. The last diagram with a single $W$ boson resonance contributes to the off-shell effects of the $W$ gauge boson.
• Figure 2: Scale dependence of the LO and NLO cross sections for the $pp\to e^+\nu_e \mu^- \bar{\nu}_\mu b\bar{b} j +X$ process at the LHC for $\sqrt{s}=8 ~{\rm TeV}$. The scale is set to a common value $\mu_{\rm R}=\mu_{\rm F}=\xi \mu_0$, where $\mu_0 = m_{\rm t}$.
• Figure 3: Transverse momentum of the hardest light jet, $\Delta R_{e^+\mu^-}$ and minimal $M_{be^+}$ for $pp\to e^+\nu_e \mu^- \bar{\nu}_\mu b\bar{b} j +X$ at the LHC with $\sqrt{s} = 8 ~{\rm TeV}$. The uncertainty bands depict the scale variation. The lower panel displays the differential K factor and its uncertainty band.