Abstract
Recent measurements of the pp → toverline{t}{W}^{pm } process in multi-lepton final states, as performed by the ATLAS collaboration in the context of the Higgs boson studies in the toverline{t}H channel, have shown discrepancies between theoretical predictions and experimental data. Such discrepancies have been observed both in the overall normalisation as well as in the modelling of the toverline{t}{W}^{pm } process. With the goal of understanding and resolving the modelling issues within the SM toverline{t}{W}^{pm } process we report on the state-of-the-art NLO QCD computation for this process. Specifically, we calculate higher-order corrections to the {e}^{+}{nu}_e{mu}^{-}{overline{nu}}_{mu }{e}^{+}{nu}_eboverline{b} and {e}^{-}{overline{nu}}_e{mu}^{+}{nu}_{mu }{e}^{-}{overline{nu}}_eboverline{b} final state at the LHC with sqrt{s} = 13 TeV. In the computation off-shell top quarks are described by Breit-Wigner propagators, furthermore, double-, single- as well as non-resonant top-quark contributions along with all interference effects are consistently incorporated at the matrix element level. Results at NLO QCD accuracy are presented in the form of fiducial integrated and differential cross sections for two selected renormalisation and factorisation scale choices and three different PDF sets. The impact of the top quark off-shell effects on the toverline{t}{W}^{pm } cross section is also examined by an explicit comparison to the narrow-width approximation.
Highlights
Computation for this e+νe μ−νμ e+νe bb and process
Analyses of ttH and ttW ± production in multi-lepton final states, which have been recently performed by the ATLAS collaboration, have shown an overall higher normalisation for the ttW ± process [3] when compared with theoretical predictions provided by OpenLoops + Sherpa [9, 10] and/or MadGraph5−aMC@NLO [11]
Even though Standard Model (SM) processes leading to same-sign lepton final states have usually very small cross sections, they are indispensable in searches for physics beyond the SM (BSM)
Summary
We compute the NLO QCD corrections to the full hadronic process pp → e+νe μ−νμ e+νe bb. The calculation of the scattering amplitudes for the qq → e+νe μ−νμ e+νe bb process is based on the well-known off-shell Dyson-Schwinger iterative algorithm that is implemented within the Helac-NLO framework [41] and in the Helac-Phegas MC program [42] The latter MC library is used to cross check all LO results. Let us note here, that among the processes of associated ttproduction which have been calculated so far with Helac-NLO (ttX, where X = j, γ, Z, W ± [56,57,58,59]), ttW ± is perhaps the simplest one in terms of computational complexity We draw this conclusion after comparing various criteria, such as the number of Feynman diagrams and subtraction terms involved in the calculation, or the number of partonic subprocesses and color structures of the amplitudes. Both the event files and the HEPlot program are available upon request and might be directly used for experimental analyses at the LHC as well as to obtain accurate SM predictions in phenomenological studies on, e.g., Higgs boson or BSM physics
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