Impact of CP Phases on Supersymmetric Processes

The main goal of the present project is the theoretical analysis of the production of super-symmetric particles at future colliders and the determination of their main parameters. Supersymmetry is at present the best motivated extension of the Standard Model. The reasons for that are mainly theoretical: With supersymmetry we can better achieve the unification of the strong, electromagnetic and weak interactions between the fundamental particles. Furthermore, supersymmetry allows us to keep the mass of the Higgs boson stable against quantum corrections. CP violation is another phenomenon, which is not completely understood. The small amount of CP violation of the Standard Model is not enough to explain the baryon asymmetry of the universe. In the supersymmetric extension of the Standard Model additional sources of CP violation can be introduced. This is another reason why supersymmetry is attractive. The ex-perimental search for supersymmetric particles has, therefore, a high priority at all present and future accelerations. If supersymmetric particles are discovered, the next important goal will be the determination of their main parameters like masses, couplings etc. Among others the deter-mination of their CP violating parameters will be very important. In order to facilitate the experimental searches as well as the determination of the supersymmetry parameters, many theoretical analyses have to be carried out. In the present project we will study how the super-symmetry parameters, in particular those responsible for CP violation, can be determined from future experiment data. For definiteness we will consider supersymmetric particle production at the ``Large Hadron Colider LHC at CERN and at a future electron-positron linear collider like TESLA. We want to add that in the past years we were the only group in Austria working in this field that successfully participated in international collaborations. We made substantial contributions to clarify the problem how supersymmetric particles can be discovered. In our study we also want to treat some problems which came up in recent international workshops and which we want to clarify. We want to achieve thefollowing goals: 1) work out which are the most suitable observables to measure the supersymmetric parameters, in particular the CP violating ones, and calculate the corresponding cross sections and decay probabilities, 2) analyze possible scenarios of mixing between slepton families and calculate lepton flavour violating signals, 3) study R-parity violating decays of supersymmetric particles and calculate their decay width.

Supersymmetric particles are hypothetical particles which have been postulated for theoretical reasons. 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. In addition to the theoretical arguments for the supersymmetric extension of the Standard Model of particle physics, supersymmetry can also provide new sources of CP violation. This is an important aspect of supersymmetry, as it gives an explanation for the observed baryon asymmetry of the universe. Supersymmetry can also provide a solution to the dark matter problem. 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. The main part of our project has been devoted to the calculation of production cross sections and decay probabilities of supersymmetric particles in the presence of CP violation. Our investigation has been carried out for a future electron-positron linear collider and for the Large Hadron Collider LHC (at CERN, Geneva). We have proposed CP sensitve observables for various supersymmetric particle processes. We have studied analytically and numerically how these CP sensitve observables depend on the underlying model parameters. Our next goal has been to show how and to which accuracy the underlying model parameters can be extracted from a set of measured observables like masses, couplings etc. This informations can then be used for an consistency check of the model. Our results will be important for designing the corresponding experiments at the future accelerators mentioned above. We have participated in several international workshops where we have reported our results. Furthermore, our group is participating in a workshop on the determination of the supersymmetry parameters, which is a joint study of theorists and experimentalists working on LHC and Linear Collider phenomenology. 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. This amounts to the calculation of so-called radiative corrections. An important topic of our project has been the systematic treatment of the radiative corrections in supersymmetric processes. In this context we have investigated also 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 have investigated in a systematic fashion the effects of virtual supersymmetric particles on observables measured in experiments. For instance, we have calculated supersymmetric conributions to the electric dipole moments of electron and neutron and to other important observables in B-physics and flavour physics. Furthermore, we have studied also supersymmetric models in which the quantum number R-parity is broken. These models provide a quantitative description of neutrino oscillations.