We study the impact of different theoretical descriptions of top quark pair production on top quark mass measurements in the di-lepton channel. To this aim, the full NLO corrections to $pp\rightarrow W^+W^-b\bar b\rightarrow (e^+ ν_e)\,(μ^- \barν_μ)\,b\bar b$ production are compared to calculations in the narrow width approximation, where the production of a top quark pair is calculated at NLO and combined with three different descriptions of the top quark decay: leading order, next-to-leading order and via a parton shower. The different theory predictions then enter the calibration of template fit functions, which are used for a fit to pseudo-data. The offsets in the top quark mass resulting from the fits based on the various theoretical descriptions are determined.
We present a full off-shell NLO QCD calculation of $pp \rightarrow e^+ ν_e b μ^- \barν_μ\bar{b} b \bar{b} + X$. Results are obtained using the HELAC-NLO Monte Carlo framework. We discuss a comparison to previous results and to experimental measurements. We also investigate the contribution of the initial states involving $b$-quarks and we introduce two $b$-jet tagging schemes.
We report on state-of-the-art theoretical predictions for $pp\to t\bar{t}b\bar{b}$ including full off-shell effects in the di-lepton decay channel at NLO QCD accuracy. We briefly discuss the impact of NLO QCD corrections on differential distributions and also asses theoretical uncertainties from scale and PDF dependence. Furthermore, we propose a simple kinematic reconstruction in order to distinguish $b$ jets originating from top-quark decays from arising from gluon splittings.
In these proceedings we discuss $t\bar{t}H$ production at the Large Hadron Collider in the Higgs characterisation model. We demonstrate the importance of off-shell effects and higher-order QCD corrections for this process and highlight the importance of single-resonant contributions for the production of a $\mathcal{CP}$-odd Higgs boson.
In light of recent tension between theory and experiment for the process ttW in the 3l channel, we present a phenomenological study of carefully chosen observables. We employ the full off-shell results at NLO QCD for ttW+ and ttW- to build the cross section ratio, an observable which is expected to exhibit enhanced perturbative stability. Furthermore, we also revisit the charge asymmetries of the top and its decay products at the fiducial integrated level. The impact of modelling is investigated for all observables.
In this proceeding we present predictions for the complete NLO QCD corrections to the production of $t\bar{t}b\bar{b}$ in the dilepton decay channel of the top quark at the LHC with $\sqrt{s}=13$ TeV. The calculation is performed considering all the full off-shell effects. Moreover, the various sources of uncertainty for this process are studied in detail. We then compare these predictions to experimental measurements. We additionally investigate the impact of the $b$-quark initiated subprocesses.
The high luminosity that will be accumulated at the LHC will enable precise differential measurements of the hadronic production of a top--antitop-quark pair in association with a $\text{W}$ boson. Therefore, an accurate description of this process is needed for realistic final states. In this work we combine for the first time the NLO QCD and electroweak corrections to the full off-shell $\text{t}\overline{\text{t}}{\text{W}}^+$ production at the LHC in the three-charged-lepton channel, including all spin correlations, non-resonant effects, and interferences. To this end, we have computed the…
The production of a single top quark in association with a $\mathrm{Z}$ boson ($\mathrm{t}\mathrm{Z}\mathrm{j}$ production) at the LHC is a relevant probe of the electroweak sector of the Standard Model as well as a window to possible new-physics effects. The growing experimental interest in performing differential measurements for this process demands an improved theoretical modelling in realistic fiducial regions. In this article we present an NLO-accurate $\mathrm{t}\mathrm{Z}\mathrm{j}$ calculation that includes complete off-shell effects and spin correlations, combining QCD and electrowea…
We present the QCD radiative corrections to the full off-shell $\rm t\bar{t}W^+$ production, considering a final state with three charged leptons, two b jets and missing energy. All interferences, off-shell effects and spin correlations are included in the calculation. Beyond presenting integrated and differential results for the full off-shell process, we compare them with those obtained applying a double-pole approximation to the virtual corrections.
NLO QCD corrections to the process $pp \rightarrow e^+ν_e μ^- \barν_μ τ^+τ^- b \bar{b}+X$ are presented with the full off-shell effects included. The calculation includes all resonant and non-resonant Feynman diagrams, photon and $Z$-gauge boson contributions, as well as interference effects, all incorporated at the matrix element level. Furthermore all heavy intermediate particles are described via Breit-Wigner propagators. Theoretical uncertainties related to the scale variation and choice of PDF sets were investigated at the integrated and differential level. The modelling is studied by a d…
The foreseen luminosities for the next LHC runs will enable precise differential measurements of the associated production of top-antitop pairs with a W boson. Therefore, providing accurate theory predictions for this process is needed for realistic final states. We present the first combination of NLO electroweak and QCD corrections to off-shell ttW$^+$ production in the three-charged-lepton channel, including non-resonant effects, full spin-correlations and interferences. Such radiative corrections comprise the electroweak and QCD corrections to the leading QCD order, and the QCD corrections…
Modern parton distribution function (PDF) determinations either neglect higher-order corrections in the electroweak (EW) coupling or implement them approximately for a subset of PDF processes. We present a new tool, PineAPPL, which supports perturbative correction in arbitrary powers of the EW and strong coupling constant, and stores theoretical predictions independently of the used PDFs in so-called interpolation grids. These are the foundation of any PDF determination, and will allow us to perform a PDF fit taking into account EW corrections for all processes consistently. Apart from PDF det…
In this contribution we report on the latest theoretical predictions for $t\bar{t}b\bar{b}$. These results are obtained for the fully decayed final state $pp \rightarrow e^+ ν_e μ^- ν_μ b \bar{b} b \bar{b}$ at next-to-leading order accuracy in QCD. We present predictions with full off-shell effects and in the Narrow Width Approximation. Specifically, we report on the size of the NLO QCD corrections and the size of the full off-shell effects. Finally, we study the nature of the $b$-jets present in the final state.
We present results of a computation of NLO QCD corrections to the production of an off-shell top--antitop pair in association with an off-shell $\text{W}^+$ boson in proton--proton collisions. As the calculation is based on the full matrix elements for the process $\text{p}\text{p}\to {\text{e}}^+ν_{\text{e}}\,μ^-\barν_μ\,τ^+ν_τ\,{\text{b}}\,\bar{\text{b}}$, all off-shell, spin-correlation, and interference effects are included. The NLO QCD corrections are about $20\%$ for the integrated cross-section. Using a dynamical scale, the corrections to most distributions are at the same level, while …
We consider the production of four charged leptons in hadron collisions and compute the next-to-leading order (NLO) QCD corrections to the loop-induced gluon fusion contribution by consistently accounting for the Higgs boson signal, its corresponding background and their interference. The contribution from heavy-quark loops is exactly included in the calculation except for the two-loop $gg\to ZZ\to 4\ell$ continuum diagrams, for which the unknown heavy-quark effects are approximated through a reweighting procedure. Our calculation is combined with the next-to-next-to-leading order QCD and NLO …
In this article, we report on the computation of the NLO QCD corrections to ${\rm p}{\rm p} \to μ^-\barν_μ{\rm e}^+ν_{\rm e}\bar{\rm b}{\rm b}\bar{\rm b}{\rm b}$ at the LHC, which is an irreducible background to ${\rm p}{\rm p}\to{\rm t}\bar{\rm t}{\rm H}\bigl(\to{\rm b}\bar{\rm b}\bigr)$. This is the first time that a full NLO computation for a $2\to8$ process with 6 external strongly-interacting partons is made public. No approximations are used, and all off-shell and interference effects are taken into account. Cross sections and differential distributions from the full computation are comp…
Recent discrepancies between theoretical predictions and experimental data in multi-lepton plus $b$-jets analyses for the $t\bar{t}W^\pm$ process, as reported by the ATLAS collaboration, have indicated that more accurate theoretical predictions and high precision observables are needed to constrain numerous new physics scenarios in this channel. To this end we employ NLO QCD computations with full off-shell top quark effects included to provide theoretical predictions for the ${\cal R}= σ_{t\bar{t}W^+}/σ_{t\bar{t}W^-}$ cross section ratio at the LHC with $\sqrt{s}=13$ TeV. Depending on the tra…
We present state-of-the-art predictions for off-shell $t\bar{t}b\bar{b}$ production with di-lepton decays at the LHC with $\sqrt{s}=13$ TeV. Results are accurate at NLO in QCD and include all resonant and non-resonant diagrams, interferences and finite-width effects for top quarks and $W$ bosons. We discuss the impact of QCD corrections and assess theoretical uncertainties from scale and PDF dependence at the integrated and differential level. Additionally we investigate the size of contributions induced by initial-state $b$ quarks to the NLO cross section.
Motivated by ongoing new physics searches in the top-quark sector at the Large Hadron Collider we report on the calculation of NLO QCD corrections to the Standard Model $pp\to t\bar{t}Z+X$ process in the tetra-lepton decay channel. This calculation is based on the matrix elements for the $e^+ ν_e\, μ^-\barν_μ\, b\bar{b} \,τ^+τ^-$ final state and includes all resonant and non-resonant Feynman diagrams, interferences and off-shell effects of the top quark as well as the $W$ and $Z$ gauge bosons. Also incorporated are photon-induced contributions. As it is customary for such studies, we show theo…
