CRC/SFB 443: Many-Body Structure of Strongly Interacting Systems

The joint research efforts of the Collaborative Research Center (SFB) 443 and the Institute for Nuclear Physics centers around the scientific exploitation of the continuous wave electron accelerator MAMI, short for Mainz Microtron. MAMI consists in its momentary stage of an injection linac and three consecutive Race Track Microtrons or RTMs accelerating the electrons in steps to 855 MeV. This stage is known as MAMI B. Electrons with this "medium energy" can be conceived as light in a microscope having just the right wave length to resolve the constituents of the nucleus, i.e. the nucleons and mesons.

The beam of MAMI excels by a very small diameter, a tiny halo, and a very good energy definition. The most important quality is, however, the effectively direct current beam (continuous wave). With such a beam it is possible to detect several coincident particles simultaneously. This allows for the usage of high beam currents and the measurement of small coincident cross sections containing significant and well defined observables.

The construction of this accelerator between 1984 to 1992 was made possible by the support of the German Research Foundation (DFG) in the form of the CRC/SFB 201. From 1992 to 1998 its topic "Medium Energy Physics with the Electromagnetic Probe" was pursued in a broad way. Of the many outstanding results just two are mentioned: the measurement of the short range correlations of nucleons in the nucleus and the electric charge distribution of the electrically neutral neutron.

On the basis of new theoretical developments (Chiral Perturbation Theory, non perturbative Quantum Chromo Dynamics QCD) it became evident that MAMI B is also very well suited for the study of the quark-gluon structure of strongly interacting particles (hadrons = {nucleons, hyperons, mesons}). This led to the installation of a new CRC/SFB titled "Many Body Structure of Strongly Interacting Systems". This new topic will be pursued in its full scope thanks to the augmentation of the energy to 1500 MeV by means of a forth stage this time in form of a Double Sided Microtron or DSM (MAMI C) granted in the frame work of the "HochschulBauFörderunGsgesetz HBFG", a law to "promote the construction at universities". It is the aim of the SFB443 to contribute to the clarification of the enigmatic permanent confinement of quarks and gluons to a volume with a diameter of 2x10-15m. For this purpose one describes the observables as form factors, polarizabilities, cross sections and polarization variables of the production of mesons, and others with theoretical models. Using these models one makes connections to QCD at low energies, i.e. in a region in which the confinement is produced and QCD is not tested.

The experiments at MAMI are performed by about 200 physicists of many countries (among others Scotland, France, Italy, The Netherlands, Belgium, USA, Japan, Russia, Slovenia) in international collaborations. These physicists are supported by a, considering the size of the facility, small but highly motivated group of engineers, technicians, secretaries etc. of about 70 persons.