The Higgs boson has a special role in the standard model. It is the only scalar particle, and via the Higgs mechanism it is responsible for the mass of all elementary particles. On July 4, 2012, the CMS and ATLAS experiments have announce the discovery of a new particle whose properties seem to be compatible with the standard model Higgs boson.
Researchers at ETP are studying various production and decay channels of the Higgs boson. ETP has contributed significantly to the analysis of the Higgs decay into a pair of tau leptons and of the decay into a pair of b quarks in associated production with a W boson. In addition we contributed to the combination of the individual Higgs-Analyses and to the Higgs decay into two W bosons. We are currently involved in analyses of associated top-Higgs production.
Top Quark Physics
The top quark is the heaviest elementary particle known today and one of the most interesting. The top quark is the only "free" quark in that it decays before it forms bound states. In many models of physics beyond the standard model, the top quarks is connected to electroweak symmetry breaking. The LHC is a "top factory": the very large production rate allows detailed studies of the top quark's properties.
At ETP we study both the electroweak production of single top quarks and QCD production of top-antitop pairs. With an analysis technique developed at ETP, we measure the charge asymmetry in top pair decays. We are also involved in the search for heavy resonances decaying into top-antitop pairs.
Search for Supersymmetry
Supersymmetry (SUSY) is an attractive and elegant theory of physics beyond the standard model: in SUSY there is a dark matter candidate, SUSY allows the unification of forces, solves the problem of quadratic divergences in the standard model and yields a natural explanation for the Higgs mechanism. However, there is no experimental evidence for supersymmetry in nature yet.
The SUSY searches at ETP concentrate on two channels. Under the assumption of large squark and small gluino masses, we search for long-lived gluinos. In electroweak production of chargino-neutralino pairs characteristic multilepton final states are expected. In both channels the LHC experiments have significantly improved existing SUSY exclusion limits.
In proton-proton collisions at the LHC, jet production is by far the dominant process. With measurements of jet observables perturbative QCD can be tested at unprecedented energy scales. Excellent understanding of jet properties at the LHC, especially their energy scale, resolution, and sub-structure is essential for precision measurements and searches for new physics.
The QCD group at ETP has contributed to the first measurements of the jet energy scale and resolution at CMS. Based on this experience, the inclusive jet cross section and two-jet and three-jet masses have been measured. A search for new physics was based on angular distributions and azimuthal decorrelation jet observables. Using the novel method of "jet areas", we conduct a measurement of the "underlying event". The sub-jet multiplicity is studied to separate quark and gluon initiated jets more efficiently.