Abstract
We present precise predictions for four-lepton plus jets production at the LHC obtained within the fully automated Sherpa+OpenLoops framework. Off-shell intermediate vector bosons and related interferences are consistently included using the complex-mass scheme. Four-lepton plus 0- and 1-jet final states are described at NLO accuracy, and the precision of the simulation is further increased by squared quark-loop NNLO contributions in the gg -> 4l, gg -> 4l+g, gq -> 4l+q, and qq -> 4l+g channels. These NLO and NNLO contributions are matched to the Sherpa parton shower, and the 0- and 1-jet final states are consistently merged using the MEPS@NLO technique. Thanks to Sudakov resummation, the parton shower provides improved predictions and uncertainty estimates for exclusive observables. This is important when jet vetoes or jet bins are used to separate four-lepton final states arising from Higgs decays, diboson production, and top-pair production. Detailed predictions are presented for the ATLAS and CMS H->WW analyses at 8 TeV in the 0- and 1-jet bins. Assessing renormalisation-, factorisation- and resummation-scale uncertainties, which reflect also unknown subleading Sudakov logarithms in jet bins, we find that residual perturbative uncertainties are as small as a few percent.
Highlights
Via gluon fusion from the vector-boson fusion (VBF) production mode
In order to describe potentially large Sudakov logarithms and related uncertainties, which arise from jet vetoes and exclusive jet bins, fixed-order predictions should be matched to parton showers or supplemented by appropriate resummations
In this publication we have presented the first results for the simulation of hadronic fourlepton plus jets production using the novel Meps@Nlo multi-jet merging technology at Next-to-leading order (NLO), and including NNLO contributions from squared quark loops
Summary
For the calculation of virtual corrections we employ OpenLoops [33], a fully automated generator of Standard-Model scattering amplitudes at one loop. The algorithm is formulated in terms of Feynman diagrams and tensor integrals, which allows for very high CPU efficiency to be achieved While this was already known from 2 → 4 NLO calculations based on algebraic methods [43,44,45,46], the idea behind OpenLoops is to replace algebraic manipulations of Feynman diagrams by a numerical recursion, which results in order-of-magnitude reductions both in the size of the numerical code and in the time needed to generate it. The first public version of the code will be released in the course of 2013
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