Higher Order Qcd Predictions for Top Quark-Physics at the LHC

Methods

We used and developed the HELAC-PHEGAS and HELAC-NLO Monte Carlo frameworks.
The former can be used to efficiently obtain amplitudes, cross sections and event samples
for arbitrary multiparticle process in the SM in leptonic, pp̄ collisions. The latter
is capable of numerically evaluating QCD virtual corrections to scattering amplitudes
and allows for a complete evaluation of NLO QCD corrections. It comprises HELAC-
1LOOP and HELAC-DIPOLES Monte Carlo programs.

Results

We have calculated NLO QCD corrections for the following processes:

• pp → ttbb in the di-lepton channel: pp → e⁺ν_e μ⁻ν_μ bb bb
• pp → ttH in the di-lepton channel: pp → e⁺ν_e μ⁻ν_μ bb H
• pp → ttZ in the multi-lepton channel: pp → e⁺ν_e μ⁻ν_μ bb τ⁺τ⁻
• pp → t¯tW+ in the multi-lepton channel: pp → e+νe μ−¯νμ b¯b τ+ντ
• pp → t¯tW− in the multi-lepton final state: pp → e+νe μ−¯νμ b¯b τ−¯ντ

Furthermore, we provided our results in the form of flexible Monte Carlo programs
and stored them in modified LES HOUCHES Files, which are then converted to Root
NTUPLE Files. We stored “events” with supplementary matrix element and PDF information.
This allows us to obtain theoretical predictions for different scale settings
and PDF choices by simply reweighting previously created files. To this end we use the
in-house software HEPLOT. Storing “events” has clear advantages when either different
observables, observable’s ranges, binning or more exclusive selection cuts are required
for example when comparing theoretical predictions with LHC data or performing other
phenomenological studies.

Discussion

NLO QCD theoretical calculations for pp → tt + X, where bb,Z,H,W^±, that we have
provided are as precise as possible and comprise all quantum effects already at the matrix
element level. In addition, we have carefully examined the size of higher-order QCD
corrections and theoretical uncertainties in such complex environments. The choice of
appropriate renormalisation and factorisation scales have been addressed to keep the
processes under excellent theoretical control. Furthermore, we have provided theoretical
results for various PDF sets which are recommended for applications at the LHC. In the
case of the pp → t¯tH process we presented predictions with possible mixing between CPeven
and CP-odd states at NLO in QCD. We compared the behaviour of the CP-even,
-odd and -mixed scenarios for the integrated fiducial cross-sections as well as several key
differential distributions. Finally, theoretical predictions for pp → t¯tb¯b in the di-lepton
channel as well as for pp → t¯tW± in the multi-lepton channel have been compared to
ATLAS data [1].

[1]
ATLAS Collaboration, Measurement of the total and differential cross-sections of t¯tW±
production in pp collisions at 13 TeV with the ATLAS detector, ATLAS-CONF-2023-019
(23 March 2023).

Additional Project Information

DFG classification: 309 Particles, Nuclei and Fields
Cluster: CLAIX

Publications

1. Giuseppe Bevilacqua, Huan-Yu Bi, Heribertus Bayu Hartanto, Manfred Kraus,
Michele Lupattelli, Malgorzata Worek
t¯tb¯b at the LHC: On the size of off-shell effects and prompt b-jet identification
Phys. Rev. D 107 (2023) 1, 014028 – Published on: 30 January 2023

2. Jonathan Hermann, Daniel Stremmer, Malgorzata Worek
CP structure of the top-quark Yukawa interaction: NLO QCD corrections and offshell
effects
JHEP 09 (2022) 138 – Published on: 19 September 2022

3. Giuseppe Bevilacqua, Heribertus Bayu Hartanto, Manfred Kraus, Jasmina Nasufi,
Malgorzata Worek
NLO QCD corrections to full off-shell production of t¯tZ including leptonic decays
JHEP 08 (2022) 060 − Published on: 03 August 2022