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Project B - Investigation of production and scattering of electroweak gauge bosons

Measurement of cross sections for electroweak gauge boson production in particular in vector boson scattering, determination of the quartic gauge boson coupling strengths and structure, derivation of limits on anomalous couplings and interpretation in extensions of the Standard Model

S. Dittmaier, G. Herten, H. Ita, K. Jakobs, M. Schumacher 

Subjects for PhD theses

 

B.1 Investigation of Vector Boson Production

  • Measurement of differential cross sections of WW production and tests of gauge boson couplings 
    (Jakobs)

    This thesis will be devoted to the investigation of the potential of the process WW→ lνqq(bar) for the measurement of WW production with the ATLAS experiment. The goal is to combine the results of this study with the ones of the channel WW→lνlν to improve the precision of measurements of differential cross sections and to maximise the sensitivity on anomalous gauge boson couplings.

 

  • Investigation of WWW- and WWZ-Production (Herten, Jakobs, Schumacher) 

    Based on a current analysis in Freiburg investigating purely leptonic final states arising from WWW production at 8 TeV we plan to study WWW and WWZ production at 13-14 TeV in several PhD theses.

    First an optimal strategy  to select and reconstruct signal events and to identify the most promising decays is to be developed. The most important challenge will be to control the background and to determine its magnitude as far as possible with data-driven methods from suitable control regions. In addition to the first measurements of the production cross sections a further goal will be to quantify possible contributions due to anomalous quartic gauge boson couplings. 

 

B.2 Investigations of Vector Boson Scattering in the Standard Model

  • Determination of Inclusive Cross Sections in Vector Boson Scattering  (Jakobs, Schumacher)

    Based on our experience in LHC Run1, initially inclusive WW production at the increased LHC centre-of-mass energy is to be investigated. The increased event rate will allow to determine differential cross sections with good precision for the first time. It is foreseen to differentiate  the final states according to the number of jets. Particular emphasis will be given to the production of a WW pair in association with two jets.  These measurements require a good understanding of the reconstruction of high energetic  jets close to the beam axis and a detailed investigation of acceptance uncertainties, which are supposed to be studied using the event generator to be developed by our colleague from theory. The cross sections measurements will be used to extract the strength of quartic gauge boson couplings assuming the tensor structure as predicted in the Standard Model

 

  • Precision predictions for the pp → WW+ 3 jets including QCD corrections (Ita)

    In the context of a PhD thesis the unitarity method will be applied to compute NLO-QCD corrections for WW+jets production. With the BlackHat library [http://arxiv.org/abs/0803.4180] key methods for the computation are available, however, the generalisations towards a wider particle spectrum including a mixture of colored and uncolored Standard-Model particles will be required. With the aim of phenomenological studies, the new matrix elements will be linked to the Sherpa Monte-Carlo program to obtain predictions for differential cross sections for the production of  two vector bosons in association with three jets at NLO accuracy in QCD. Finally, the results will be linked to the parton shower of Sherpa. As a first phenomenological study the influence of vector-boson-fusion cuts on the theoretical uncertainties of exclusive observables with jet-vetos will be investigated. 

 

 B.3 Investigations of Vector Boson Scattering beyond the Standard Model 

  • Determination of structure and stregth of non-standard coupling terms in vector-boson scattering (Dittmaier, Jakobs, Schumacher)

    At the interface between theory and experiment we will offer PhD projects focusing on model-independent investigations of vector-boson scattering in the effective field theory based on Standard Model couplings and SU(3)xSU(2)xU(1)-symmetric dimension-6 operators. The parametrization and evaluation of the effective field theory will follow the conventions of the LHC Higgs Cross Section Working Group, to allow for a coherent phenomenological picture in combination with analyses of the Higgs boson.

    On the theoretical side, we will generalize Standard Model predictions to the effective field theory and provide them in the form of Monte Carlo programs, where at least quantum corrections of the strong interactions are included.

    In collaboration between theory and experiment, we will work out appropriate observables and assess their sensitivity to effective coupling terms, carefully investigating theoretical uncertainties.

    On the experimental side, we will dedicate PhD projects to the structure and strength of non-standard couplings in vector-boson scattering employing measured rates and distributions of the optimized observables mentioned above. The analyses, in particular, require new optimizations of event selections, in order to identify specific phase-space regions with high purity.
     
  • Generalization of Standard Model predictions to extended models (Dittmaier)

    In a PhD project, theoretical predictions that are currently worked out in the working group Dittmaier at the NLO level in the Standard Model will be generalized to models with extended or alternative Higgs sectors (Higgs singlets, more Higgs doublets, Higgs triplets, etc.).
     
  • Experimental Analyses of Vector Boson Scattering in Extensions of the Standard Model (Jakobs, Schumacher)

    An experimental PhD thesis will be devoted to the determination of model parameters and coupling structures  in specific extensions of the Standard Model.  In the interpretation within specific models of New Physics we also expect large synergies due to parallel studies of such models using observables from Higgs boson production and vector boson scattering, respectively. 

 

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