Interpretation of LHC data with Simplified Models

We propose to perform a re-interpretation of LHC results in the context of various physics scenarios beyond the standard model (BSM) based on simplified models spectra (SMS). SMS are effective models which introduce only a limited set of new particles. They are intended to describe both the negative and the positive results of the searches for BSM physics in the language of theoretical physics. Statements about the underlying physics can then be inferred without the need for detailed knowledge about the experiments` analyses. The goal of our work is to identify and describe regions in model parameter space that can in principle be excluded but are currently not covered by any analysis, to assess the status of the search for a "natural" solution to the gauge hierarchy problem in light of both the CMS and the ATLAS SMS results, and to give feedback to the experimental search groups about which paths towards new physics are still worth pursuing. In the case of positive search results, we will furthermore describe the potential signal in terms of simplified models, and will make suggestions where to search next. We have developed a prototype "SModelS" framework, which performs the decomposition of a BSM model into its simplified models spectrum. It then compares the individual SMS topologies with our database of experimental results. In this project we want to bring the the SModelS framework to fruition: we will develop it from a prototype to a production grade tool and apply it systematically to BSM models, starting with a natural supersymmetric theory. To augment the sensitivity of our approach, we will reimplement some of the published analyses and interpret them in the context of additional simplified models. In this project we also will also introduce the SModelS framework in the "Fittino" effort. Fittino is a project which performs "global fits" of fundamental models to several LHC search results by reimplementing the analyses outside the experimental collaborations. In a first step, the SModelS framework will be employed as a simple diagnostic tool, to select the list of experimental analyses relevant for a particular model in a more systematic manner. In a subsequent step, we will use the simplified models results more comprehensively: we will replace the concept of 95% confidence level upper limits with a more sophisticated statistical approach based on likelihoods and make direct use of the SMS results in the Fittino framework. For the second half of the project we expect to have experimental results from LHC runs at 13 TeV available. We will maintain and extend our results database and publish updates to the previously mentioned efforts with the LHC13 data. Our ultimate vision is to construct the "next standard model" in a bottom-up fashion from SMS results.

When in July 2012, the discovery of the Higgs boson was announced, a decades-long era of searching for the last missing piece of the Standard Model of particle physics has come to an end. Its discovery, however, begs to ask the next fundamental question: why is the mass of the Higgs boson so small? Is there a mathematical mechanism that stabilizes it against quantum mechanical contributions emerging from physics at high energy scales? At that time, the most plausible answer was supersymmetry; that is, a theoretical framework that introduces a fundamental symmetry between fermionic matter particles and bosonic energy particles.Both types of particles would contribute equally to the mass of the Higgs boson, albeit with different signs, thus canceling each other and stabilizing the Higgs mass. This idea predicted that supersymmetric particles be found at the LHC; but no such signals appeared in the data.Is, as a consequence, the framework of supersymmetry to be abandoned entirely? Shall we look for alternatives? Or shall we give up on the notion of a natural answer to the Higgs hierarchy problem and just accept the idea that our universe seems like a special place? Within the scope of this project, we gave some answers to such questions. Introducing the notion of ,,simplified models spectra" (SMS) we developed a software framework SModelS that takes fundamental theories like supersymmetry and decomposes them into fundamental ,,building blocks". These can then be matched against our newly created database of SMS results from the LHC experiments, with a final statement on whether or not the theory at hand is compatible with LHC data. We finally applied our newly created software to modern theoretical frameworks and discussed the results in a peer-review publication. By now, SModelS is gaining acceptance in the community. It is our hope that we can build on these successes in future projects; after all, it is our final goal to use SModelS to systematically build up the hypothetical ,,Next Standard Model" in a bottom-up fashion, starting from LHC data.