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Register a new userPolarized electroweak bosons in ${bf text{W}^+text{W}^-}$ production at the LHC including NLO QCD effects
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The measurement of polarization fractions of massive gauge bosons at the LHC provides an important check of the Standard Model and in particular of the Electroweak Symmetry Breaking mechanism. Owing to the unstable character of $text{W}$ and $text{Z}$ bosons, devising a theoretical definition for polarized signals is not straightforward and always subject to some ambiguity. Focusing on $text{W}$-boson pair production at the LHC in the fully leptonic channel, we propose to compute polarized cross-sections and distributions based on the gauge-invariant doubly-resonant part of the amplitude. We include NLO QCD corrections to the leading quark-induced partonic process and also consider the loop-induced gluon-initiated process contributing to the same final state. We present results for both an inclusive setup and a realistic fiducial region, with special focus on variables that are suited for the discrimination of polarized cross-sections and on quantities that can be measured experimentally.
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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 $text{p}text{p}to {text{e}}^+ u_{text{e}},mu^-bar{ u}_mu,tau^+ u_tau,{text{b}},bar{text{b}}$, 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 some distributions show much larger $K$-factors in suppressed regions of phase space. We have performed a second calculation based on a double-pole approximation. While the corresponding results agree with the full calculation within few per cent for integrated cross-sections, the discrepancy can reach $10%$ and more in regions of phase space that are not dominated by top--antitop production. As a consequence, on-shell calculations should only be trusted to this level of accuracy.
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 NLO electroweak radiative corrections to the leading QCD order as well as the NLO QCD corrections to both the QCD and the electroweak leading orders.
We study the impact of anomalous gauge boson and fermion couplings on the production of $W^+W^-$ pairs at potential future LHC upgrades and estimate the sensitivity at $sqrt{S}=14$ TeV with $3~ab^{-1}$ and $sqrt{S}=27$ TeV with $15~ab^{-1}$. A general technique for including NLO QCD effects in effective field theory (EFT) fits to kinematic distributions is presented, and numerical results are given for $sqrt{S}=13$ TeV $W^+W^-$ production. Our method allows fits to anomalous couplings at NLO accuracy in any EFT basis and has been implemented in a publicly available version of the POWHEG-BOX. Analytic expressions for the $K$-factors relevant for $13$ TeV total cross sections are given for the HISZ and Warsaw EFT bases and differential $K$-factors can be obtained using the supplemental material. Our study demonstrates the necessity of including anomalous $Z$- fermion couplings in the extraction of limits on anomalous 3-gauge-boson couplings.
We compute the NLO QCD corrections to the loop-induced gluon fusion contribution in $W^+W^-$ production at the LHC. We consider the full leptonic process $ppto ell^+ell^{prime, -} u_{ell}{bar u}_{ell^prime}+X$, by including resonant and non-resonant diagrams, spin correlations and off-shell effects. Quark-gluon partonic channels are included for the first time in the calculation, and our results are combined with NNLO predictions to the quark annihilation channel at the fully differential level. The computed corrections, which are formally of ${cal O}(alpha_{mathrm{S}}^3)$, increase the NNLO cross section by only about 2%, but have an impact on the shapes of kinematical distributions, in part due to the jet veto, which is usually applied to reduce the top-quark background. Our results, supplemented with NLO EW effects, provide the most advanced fixed-order predictions available to date for this process, and are compared with differential ATLAS data at $sqrt{s}=$ 13 TeV.
We present an implementation of electroweak W+W-jj production at hadron colliders in the POWHEG framework, a method that allows the interfacing of a next-to-leading order QCD calculation with parton shower Monte Carlo programs. We provide results for both, fully and semi-leptonic decay modes of the weak bosons, taking resonant and non-resonant contributions and spin correlations of the final-state particles into account. To illustrate the versatility of our implementation, we provide phenomenological results for two representative scenarios with a light and with a heavy Higgs boson, respectively, and in a kinematic regime of highly boosted gauge bosons. The impact of the parton shower is found to depend on the setup and the observable under investigation. In particular, distributions related to a central-jet veto are more sensitive to these effects. Therefore the impact of radiation by the parton shower on next-to-leading order predictions should be assessed carefully on a case-by-case basis.
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