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Nikolas Kauer
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Theoretical predictions for scattering processes with multi-particle final states at next-to-leading order (NLO) in perturbative QCD are essential to fully exploit the physics potential of present and future high-energy colliders. The status of NLO QCD calculations and tools is reviewed.
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We study WZ production with anomalous couplings at $bar{n}$NLO QCD using the LoopSim method in combination with the Monte Carlo program VBFNLO. Higher order corrections to WZ production are dominated by additional hard jet radiation. Those contributions are insensitive to anomalous couplings and should thus be removed in analyses. We do this using a dynamical jet veto based on the transverse energy of the QCD and EW final state particles. This removes jet dominated events without introducing problematic logs like a fixed $p_{text{T}}$ jet veto.
We report on the activities of the ``QCD Tools for heavy flavors and new physics searches working group of the Run II Workshop on QCD and Weak Bosons. The contributions cover the topics of improved parton showering and comparisons of Monte Carlo programs and resummation calculations, recent developments in Pythia, the methodology of measuring backgrounds to new physics searches, variable flavor number schemes for heavy quark electro-production, the underlying event in hard scattering processes, and the Monte Carlo MCFM for NLO processes.
We study the production of the four-lepton final state $l^+ l^- l^+ l^-$, predominantly produced by a pair of electroweak Z bosons, ZZ. Using the LoopSim method, we merge NLO QCD results for ZZ and ZZ+jet and obtain approximate NNLO predictions for ZZ production. The exact gluon-fusion loop-squared contribution to the ZZ process is also included. On top of that, we add to our merged sample the gluon-fusion ZZ+jet contributions from the gluon-gluon channel, which is formally of N^3LO and provides approximate results at NLO for the gluon-fusion mechanism. The predictions are obtained with the VBFNLO package and include the leptonic decays of the Z bosons with all off-shell and spin-correlation effects, as well as virtual photon contributions. We compare our predictions with existing results for the total inclusive cross section at NNLO and find a very good agreement. Then, we present results for differential distributions for two experimental setups, one used in searches for anomalous triple gauge boson couplings, the other in Higgs analyses in the four charged-lepton final state channel. We find that the approximate NNLO corrections are large, reaching up to 20% at high transverse momentum of the Z boson or the leading lepton, and are not covered by the NLO scale uncertainties. Distributions of the four-lepton invariant mass are, however, stable with respect to QCD corrections at this order.
Accessing the polarization of weak bosons provides an important probe for the mechanism of electroweak symmetry breaking. Relying on the double-pole approximation and on the separation of polarizations at the amplitude level, we study WZ production at the LHC, with both bosons in a definite polarization mode, including NLO QCD effects. We compare results obtained defining the polarization vectors in two different frames. Integrated and differential cross-sections in a realistic fiducial region are presented.
We present applications of the program GoSam for the automated calculation of one-loop amplitudes. Results for NLO QCD corrections to beyond the Standard Model processes as well as Higgs plus up to three-jet production in gluon fusion are shown. We also discuss some new features of the program.
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