Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

NLO QCD corrections to the production of t-tbar-Z in gluon fusion

Achilleas Lazopoulos, Kirill Melnikov, Frank Petriello

TL;DR

This paper computes the next-to-leading order QCD corrections to the gluon-fusion subprocess gg → t tbar Z, the dominant component of pp → t tbar Z at the LHC. It uses sector decomposition with contour deformation and two-cut slicing to obtain finite virtual and real-emission contributions, renormalizes in the MSbar scheme with on-shell top mass and wavefunction, and employs MRST PDFs. The findings show large positive NLO corrections (up to ~75%) and a significant reduction in scale uncertainty to about ±5%, with the Z transverse momentum distribution largely preserving shape. This work constitutes a crucial step toward a full NLO prediction for ttZ production and constrains top electroweak couplings, with planned extension to include quark-initiated channels.

Abstract

We compute the O(alpha_s) QCD corrections to the partonic process gg -> t-tbar-Z at the LHC. This partonic channel is the dominant component of the scattering process pp -> t-tbar-Z, which will be important for measuring the t-tbar-Z electroweak couplings. The O(alpha_s) corrections increase the total cross section by up to 75% for reasonable choices of the renormalization and factorization scales. Inclusion of these contributions descreases the residual scale dependence of the cross section coming from uncalculated higher order terms to +-5%.

NLO QCD corrections to the production of t-tbar-Z in gluon fusion

TL;DR

This paper computes the next-to-leading order QCD corrections to the gluon-fusion subprocess gg → t tbar Z, the dominant component of pp → t tbar Z at the LHC. It uses sector decomposition with contour deformation and two-cut slicing to obtain finite virtual and real-emission contributions, renormalizes in the MSbar scheme with on-shell top mass and wavefunction, and employs MRST PDFs. The findings show large positive NLO corrections (up to ~75%) and a significant reduction in scale uncertainty to about ±5%, with the Z transverse momentum distribution largely preserving shape. This work constitutes a crucial step toward a full NLO prediction for ttZ production and constrains top electroweak couplings, with planned extension to include quark-initiated channels.

Abstract

We compute the O(alpha_s) QCD corrections to the partonic process gg -> t-tbar-Z at the LHC. This partonic channel is the dominant component of the scattering process pp -> t-tbar-Z, which will be important for measuring the t-tbar-Z electroweak couplings. The O(alpha_s) corrections increase the total cross section by up to 75% for reasonable choices of the renormalization and factorization scales. Inclusion of these contributions descreases the residual scale dependence of the cross section coming from uncalculated higher order terms to +-5%.

Paper Structure

This paper contains 5 sections, 3 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Notation and the leading order cross section
  3. Next-to-leading order computation
  4. Results
  5. Conclusions

Figures (3)

  • Figure 1: Sample diagrams for $gg \to t \bar{t} Z$ appearing at leading order.
  • Figure 2: Sample diagrams for the ${\cal O}(\alpha_s)$ virtual corrections to $gg \to t \bar{t} Z$.
  • Figure 3: Left panel: the transverse momentum distribution of the $Z$-boson at leading order and next-to-leading order in $\alpha_s$. Right panel: the dependence of the $K$-factor defined as $K = {\rm d}\sigma_{\rm NLO}/{\rm d}\sigma_{\rm LO}$ on the transverse momentum of the $Z$-boson. We set $\mu = \mu_0/2$ in both plots.