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[en] The International Linear Collider is now proposed with a staged machine design, with the first stage at =250 GeV and an integrated luminosity goal of 2 ab. One of the questions for the machine design is the importance of positron polarization. In this report, we review the impact of positron polarization on the physics goals of the 250 GeV stage of the ILC and demonstrate that positron polarization has distinct advantages.
[en] This is a status report of the WHIZARD Monte Carlo multi-purpose event generator given at the LCFORUM 2012 at DESY. I review here the development of the WHIZARD generator version 2 with a special emphasis on linear collider physics. In case you use the program, please do cite the official reference(s).
[en] The discovery of a 126 GeV resonance at the LHC has opened a new era of particle physics. In light of this discovery, it has become of central importance a deeper understanding of the underlying mechanism of electroweak symmetry breaking associated to the observed resonance. An appealing alternative to the common Supersymmetric extension of the SM, is the idea that the Higgs is a pseudo-Goldstone boson: Little Higgs models provide plausible realizations of this scenario with the feature that they cancel all quadratically divergent contributions to the Higgs mass at one-loop. In this talk we are going to present the updated allowed contours in the parameter space of different Little Higgs models in light of the 7+8 TeV LHC data collected in 2011-2012.
[en] The status of the most prominent model implementations of the Little Higgs paradigm, the Littlest Higgs with and without discrete T parity as well as the Simplest Little Higgs are reviewed. For this, we are taking into account a fit to 21 electroweak precision observables from LEP, SLC, Tevatron together with the full 25 fb-1 of Higgs data reported from ATLAS and CMS at Moriond 2013. We also - focusing on the Littlest Higgs with T parity - include an outlook on corresponding direct searches at the 8 TeV LHC and their competitiveness with the EW and Higgs data regarding their exclusion potential. This contribution to the Snowmass procedure serves as a guideline which regions in parameter space of Little Higgs models are still compatible for the upcoming LHC runs and future experiments at the energy frontier. For this we propose two different benchmark scenarios for the Littlest Higgs with T parity, one with heavy mirror quarks, one with light ones.
[en] The Littlest Higgs model with T-parity is providing an attractive solution to the fine-tuning problem. This solution is only entirely natural if its intrinsic symmetry breaking scale f is relatively close to the electroweak scale. We examine the constraints using the latest results from the 8 TeV run at the LHC. Both direct searches and Higgs precision physics are taken into account. The constraints from Higgs couplings are by now competing with electroweak precision tests and both combined exclude f up to 694 GeV. At the same time limits from direct searches now become competitive and constrain f to be larger than 638 GeV. We show that the Littlest Higgs model parameter space is slowly driven into the TeV range. Furthermore, we develop a strategy on how to optimise present supersymmetry searches for the considered model, with the goal to improve the constraints and yield more stringent limits on f.
[en] To test physics beyond the Standard Model (SM) at the LHC in a model-independent way, we studied an Effective Field Theory (EFT) consisting of the SM with additional dimension-6 operators. Using a special basis for the operators, the GIMR basis, we implemented the complete set of dim-6 operators into the Monte Carlo Event Generator WHIZARD. Focusing on electroweak boson observables, we show preliminary results for LHC Run II at 13 TeV.
[en] Measuring mass and spin of new particles is of crucial importance for the understanding of general new physics models. We present two scenarios in which determination methods suffer from large uncertainties: the introduction of exotic particle content in B(MS)SM models as well as broadening effects due to off-shell contributions give rise to the distortion of kinematic distributions in an LHC environment. Consequently, this may not only affect determination of model parameters, but it can also impose a confusion with combinatorical effects of the underlying analysis. A correct treatment and modeling of these effects is thus indispensable for the ability to disentangle between different alternative BSM scenarios.
[en] In this paper, we investigate how a sizeable width-to-mass ratio for a gluino, as is for example realized in GMSB scenarios, could affect the discovery potential of gluinos at the LHC. More importantly, the influence of the gluino being ''fat'' on the standard mass and spin determination methods at the LHC are investigated. For this purpose, we focus on gluino production at the LHC, where we do not factorize the first step in the gluino decay cascade, but treat the following decay cascade steps in factorization, including full spin correlations. The effects of sizeable width-to-mass ratios from a few up to 15-20 per cent on the endpoint of several mass determination methods as well as on means for discrimination between BSM spin paradigms like SUSY and UED are studied. (orig.)
[en] In order to cope with increased experimental accuracy of the LHC era, the accuracy of theoretical predictions has to be increased as well. For this task, sophisticated tools for automated computation, namely matrix-element generators and Monte-Carlo event generators, have to take next-to-leading order effects into account. A hadronic initial state like protons at the LHC however incorporates computational challenges such as infrared initial state divergences. A possibility to substract these divergencies is the Frixione-Kunszt-Signer (FKS) subtraction scheme whose implementation in Whizard is currently being validated. In this talk I will show details of the implementation and validation of the FKS subtraction, particularly the initial state splittings and regions, using as a prime example computed by Whizard the simplest process where all these components are needed, namely pp Zj+X at QCD NLO.