Particle physics probes the basic building blocks of matter and their interactions, which determine the structure and properties of the extreme diversity of matter in the universe. The web portal makes the fascinating research understandable to an interested public.more

Image: ESO, R. Fosburymore

Beyond the standard model

Supersymmetry is a model explaining matter and forces beyond the standard model, but which has not been confirmed by any experiment so far. It turns out that the so-called dark matter could be well explained in the context of this theory. Dark matter is a form of matter that comes up to now only indirectly into the picture, namely in the measurement of the stars' velocities in galaxies as well as in the observation of the cosmic background radiation by satellites. It was, by the way, the brilliant Swiss physicist Fritz Zwicky who first suggested the presence of dark matter in 1933 already.

The advocates of supersymmetry believe that dark matter could be explained by a supersymmetric particle. Supersymmetric particles can be pictured as mirror particles of the known elementary particles. There is hence a selectron for the electron, and a squark for the quark. The supersymmetric counterpart of a matter particle would always be a force particle, and the supersymmetric counterpart of a force particle a matter particle. Furthermore, supersymmetry requires the existence of five different Higgs particles, three neutral and two charged ones. All five of them have in addition their own supersymmetric counterparts, the so-called Higgsinos.

A subtle combination between the supersymmetric counterparts of the force particles and the neutral Higgsinos would readily have the qualities that scientist expect from dark matter: it would be stable, electrically neutral and would only interact extremely weakly with normal matter. Even though it arises as a combination, one has here as a matter of fact an elementary particle that combines the various properties. There are also further combinations between the supersymmetric counterparts of force particles and Higgsinos. These are however not stable, and some are also charged – and therefore do not come in consideration for the explanation of dark matter.

Supersymmetric particles have not been detected in experiments so far. This fact indicates that such particles – if they exist – must have a large mass. Does supersymmetry actually describe part of the reality? An answer to this question could emerge from the precision study of the Higgs particle during the coming months at the LHC in Geneva.