Electroweak and QCD corrections to top-pair hadroproduction in association with heavy bosons

S Frixione,M Zaro,V Hirschi,D Pagani,H.-S Shao

doi:10.1007/jhep06(2015)184

Abstract

We compute the contribution of order $\alpha_S^2\alpha^2$ to the cross section of a top-antitop pair in association with at least one heavy Standard Model boson -- $Z$, $W^\pm$, and Higgs -- by including all effects of QCD, QED, and weak origin and by working in the automated MadGraph5_aMC@NLO framework. This next-to-leading order contribution is then combined with that of order $\alpha_S^3\alpha$, and with the two dominant lowest-order ones, $\alpha_S^2\alpha$ and $\alpha_S\alpha^2$, to obtain phenomenological results relevant to a 8, 13, and 100~TeV $pp$ collider.

Highlights

While at present the precision of the theoretical predictions is sufficient for all kind of phenomenological applications, since one is dominated by experimental uncertainties, the Run II of the LHC, with both energy and luminosity larger than in Run I, might soon change the situation, whence the need to increase the precision of the perturbative predictions
In HBR processes, the transverse momentum of the vector boson denoted by X in eq (2.5) is not constrained; this implies that, in the case of identical particles (X = V ), a single vector boson fulfilling the last condition in eq (3.1) is sufficient for the corresponding event to contribute to the cross section
The O(αS2α2) results for ttH production had been previously presented in the literature in refs. [31, 32]; those for ttZ, ttW +, and ttW − are given here for the first time. These top-antitop-heavy boson system M (ttV) processes are characterised by tiny cross sections, the total rates being smaller than 1 pb at LHC energies, and of the order of 10 pb at a 100-TeV collider

Summary

Introduction

While at present the precision of the theoretical predictions is sufficient for all kind of phenomenological applications, since one is dominated by experimental uncertainties, the Run II of the LHC, with both energy and luminosity larger than in Run I, might soon change the situation, whence the need to increase the precision of the perturbative predictions At fixed order, this can be done in two ways: by computing either the NNLO QCD corrections, or the NLO electroweak (EW) ones; these, as a rule of thumb, are believed to have comparable numerical impacts. Calculations at the NNLO in QCD for processes of the complexity of ttV production are beyond the scope of the currently available technology This is not the case for NLO EW corrections, and the aim of this paper is to compute them. We shall retain in our computation the two dominant terms at the LO and NLO, namely ΣLO,, ΣLO,, ΣNLO,, and ΣNLO,

Objectives

Results

Conclusion