Resonant top pair production at NLO in QCD

Diogo Buarque Franzosi

doi:10.1051/epjconf/201715802006

Abstract

We compute the contribution of a scalar H or pseudo-scalar A resonance in top-quark pair production at NLO accuracy in QCD including the interference between pure QCD SM diagrams and the resonant p p → A H → t t process which drastically modifies the lineshape of the signal from a simple peak to peak-dip structure. We assume a point-like coupling between scalar and the gluons in a consistent effective field theory framework and improve the results with reweighting techniques in the case of resolved fermion loops in the production. The computation is set in an automatic framework and can be used to produce showered unweighted events. The detailed study is presented in Ref [1].

Highlights

Scalar resonances decaying into a ttsystem exist in many BSM scenarios
We compute the contribution of a scalar H or pseudo-scalar A resonance in top-quark pair production at NLO accuracy in QCD including the interference between pure QCD SM diagrams and the resonant pp → A(H) → ttprocess which drastically modifies the lineshape of the signal from a simple peak to peak-dip structure
The NLO QCD corrections to the interference between signal and background in resonant scalar or pseudoscalar top pair production have been computed using an effective field theory (EFT) approach without any approximations. In this way we obtained accurate predictions for the ttlineshape for the case in which gluon fusion scalar production is dominated by heavy particles running in the loop or strong dynamics generating point-like interaction between the scalars and the gluon

Summary

Introduction

Scalar resonances decaying into a ttsystem exist in many BSM scenarios. In order to correctly describe this process at the LHC, and to determine the constraints on the parameters of different models, it is important to get trustworthy and robust theoretical predictions. It is well known that the interference between resonant signal and the QCD background can drastically modify the lineshape of the signal, from a single peak to a dip-peak structure, and may be even larger than the pure signal It appears to receive similar QCD corrections, as indicated by estimates in an effective field theory (EFT) approach in the soft gluon approximation [2], and in a simplified K-factor derived from the geometric mean of the background and signal K-factors [3]. Our NLO computation of the interference is based on the EFT framework, which in the unresolved case provides accurate results (i.e. without using soft-gluon approximation), and in the resolved case, can be further improved by using reweighting techniques These results will be passed to PS simulation, to obtain more realistic predictions

Theoretical setup

Benchmarks and results

Benchmark A

Benchmark B

Benchmarks C1 and C2

Conclusions