CERN-TH-18-039
CERN-TH-2018-039
IPPP/18/13
MCnet-18-05
arXiv:1803.00950
IPPP-18-13
MCNET-18-05
Eur.Phys.J. C78 (2018) 317

by: Gütschow, Christian (University Coll. London) et al.

Abstract:
We present theoretical predictions for the production of top-quark pairs in association with jets at the LHC including electroweak (EW) corrections. First, we present and compare differential predictions at the fixed-order level for $t\bar{t}$ and $t\bar{t}+\text {jet}$ production at the LHC considering the dominant NLO EW corrections of order ${{\mathcal {O}}}(\alpha _\mathrm {s}^2 \alpha )$ and ${{\mathcal {O}}}(\alpha _\mathrm {s}^3 \alpha )$ respectively together with all additional subleading Born and one-loop contributions. The NLO EW corrections are enhanced at large energies and in particular alter the shape of the top transverse momentum distribution, whose reliable modelling is crucial for many searches for new physics at the energy frontier. Based on the fixed-order results we motivate an approximation of the EW corrections valid at the percent level, that allows us to readily incorporate the EW corrections in the MePs@Nlo framework of Sherpa combined with OpenLoops. Subsequently, we present multi-jet merged parton-level predictions for inclusive top-pair production incorporating NLO QCD + EW corrections to $t\bar{t}$ and $t\bar{t}+\text {jet}$ . Finally, we compare at the particle-level against a recent 8 TeV measurement of the top transverse momentum distribution performed by ATLAS in the lepton + jet channel. We find very good agreement between the Monte Carlo prediction and the data when the EW corrections are included.