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CMS Physics Analysis

 

The CMS analysis group at HEPHY uses data from proton-proton collisions that are produced in CERN's Large Hadron Collider (LHC) at the highest energies that can currently be achieved. The particles generated in these collisions are recorded by the CMS experiment and allow the extension of our knowledge of elementary particles and the forces acting between them.

One of the priorities of research at the LHC is the search for new particles and processes, which are not predicted by the current "standard model" of particle physics. The discovery of a Higgs boson at the LHC has completed this model and essentially validated its predictions. However, it has several shortcomings, with the lack of an explanation for "dark matter" as one of the most prominent ones.

The CMS analysis group at HEPHY has a leading role in the search for evidence for extensions of the standard model. Different approaches are used: the direct search for new particles that could be generated in the collisions, and the indirect search using precision measurements and comparison with the predictions of the standard model.

 

Research interests

The activities of the analysis group are focused on the following areas:

  • Direct search for "new physics": Our studies in this area are motivated by supersymmetry, a theory that predicts a new partner particle for each particle of the standard model. In a search for the partners of the gluons a wide range of masses could be excluded. Several analyses focus on the supersymmetric partners of the top quark, since the presence of these particles could have an impact on the mass of the Higgs boson and the abondance of dark matter in the universe.
    In collaboration with HEPHY's theory group we have also developed a framework that allows the comparison of the predictions of other, new models with the above-mentioned as well as other LHC results.
     
  • Physics of the Higgs boson: Current measurements of the properties of this particle, which was discovered in 2012, are compatible with the predictions of the standard model. However, their precision is still limited. Interactions of the Higgs boson with tau leptons are an important handle for distinguishing the predictions of the standard model from those of other, extended theories. Therefore the group at HEPHY studies decays into pairs of tau leptons. Recently the first observation of this decay mode by a single experiment was demonstrated.
     
  • Quantum chromodynamics: our studies in this area target a better understanding of quantum chromodynamics (QCD) - the theory of the strong interaction, which is the central element at a hadron collider like LHC and also relevant for the background determination for the analyses mentioned above. We use the production rate and the spin orientation of quarkonia - bound states of a heavy quark with its anti-particle - to verify the predictions of QCD calculations.