Supersymmetric Processes at Future Colliders

Supersymmetry plays a crucial role in the search for a grand unified theory of all fundamental forces. The supersymmetric extension of the standard model is nowadays one of the most attractive possibilities to incorporate the theories of strong, electromagnetic, and weak interactions in a complete and consistent way. Supersymmetry predicts a new particle for each known particle, the so-called superpartner. The experimental search for these superpartners has a high priority at present accelerators and will gain even more importance at future colliders. In this project we want to calculate the production of supersymmetric particles for existing and proposed colliders. The goal of this investigation is to clarify how these hypothetical particles can be discovered in experiment. We want to calculate the production cross sections and decay widths of the supersymmetric particles for the "Large Hadron Collider" (LHC), located at CERN, for the designed linear electron-positron collider with a centre of mass energy of 0.5-2.0 TeV and the proposed muon collider with a centre of mass energy of 0.5-4.0 TeV. These predictions are essential to design and carry out these experiments. In the past years we were the only group in Austria that successfully participated in international collaborations and workshops in this field, and thus we contributed significantly to the clarification of the problem how supersymmetric particles can be discovered in experiments. The questions to be answered by the present project were raised in different international workshops. We want to achieve the following goals: 1)obtain predictions for production cross sections and decay widths of supersymmetric particles and Higgs bosons including loop corrections 2)investigate the effects of the additional CP violating parameters that are due to supersymmetry 3)calculate the decay widths of supersymmetric particles in the case of R-parity violation

Supersymmetric particles are hypothetical particles which have been postulated for theoretical reasons. For example, one reason is that in supersymmetric theories of particle physics it is easier to understand the unification of all fundamental forces than in non-supersymmetric theories. The experimental search for these supersymmetric particles is one of the most urgent tasks at all present and future high energy accelerators. The main goal of our research project has been to carry out those theoretical investigations which are necessary for understanding how to search for supersymmetric particles and how to study their properties at future colliders. A main part of our project has been the calculation of production cross sections and decay probabilities of supersymmetric particles at the electron-positron storage ring LEP and at the Large Hadron Collider LHC (at CERN, Geneva), as well as at a future electron-positron linear collider and at a future muon collider. We calculated the masses of the supersymmetric particles and their other properties as following from certain model parameters. We studied analytically and numerically how the production and decay rates depend on these model parameters. Our results will be important for designing the corresponding experiments at the future accelerators mentioned above. We also participated in several international workshops. Owing to our experience in this field we were asked to collaborate in writing-up the Technical Design Report for the future electron-positron linear collider TESLA. This Technical Design Report has been submitted to the German Government in March 2001 and it will be the basis for all further decisions concerning this new accelerator. There is no doubt that a very high experimental precision will be reached at the future accelerators. Correspondingly, the precision of the theoretical predictions must also be very high. In the precision calculation of some observables, therefore, it is necessary to take into account in a systematic way certain theoretical corrections, the so-called radiative corrections. An important topic of our project has been the sytematic treatment of the radiative corrections in supersymmetric processes, as well as the development of new analytical concepts and calculational techniques. In this context we also investigated supersymmetric processes involving the Higgs bosons. These are also hypothetical particles, whose discovery would allow us to understand in a better way the origin of the masses of the various elementary particles. Finally we would like to remark that we systematically investigated also the effects of virtual supersymmetric particles. In this context we want to mention our analyses of possible new phenomena in CP violation and of certain rare decays of the B mesons. Furthermore, we also studied supersymmetric models in which the quantum number R-parity is broken.