The main topic of the research project is the structure of hadrons and
their interactions. These are particles which participate in the
strong interaction, which is one of the four fundamental forces of nature,
described by Quantum-Chromo Dynamics. The best known examples are the proton
and the neutron (called nucleons), which are the building blocks of atomic
nuclei. Hadrons are composed of elementary particles called quarks. All
hadrons known up to now belong to one of two different classes, the baryons
(among them protons and neutrons), which are composed of three quarks and
the mesons (instable, short lived particles), which are made of
quark - antiquark pairs. Unlike any other composite system, most of the
mass of hadrons is generated by dynamical effects from the interaction of
the quarks. As an example, the sum of the masses of the three quarks forming
nucleons, contributes only about 0.6% - 1.8% to the mass of the nucleon.
This means, that more than 98% of the mass of ordinary matter arise from
dynamical effects of the strong interaction. The structure of hadrons is
thus intimately related to the properties of the strong interaction.

Recently, due to the large progress in the field of lattice QCD and chiral
perturbation theory, a much more solid connection between experimental
observations and the fundamental properties of QCD started to emerge.
However, up to now even the excitation spectrum of the nucleon is far from
being understood. It is still out of reach for lattice calculations and
quark models predict much more excited states than have been observed.
Most of those states have been observed with hadron induced reactions, in
particular elastic scattering of charged pions. It is thus possible that the
data base is biased for states that couple only weakly to pions.

However, the large progress in accelerator and detector technology,
now allows to study the electromagnetic excitation of resonances via photon
induced reactions, in particular photoproduction of mesons, with comparable
precision, although the cross sections are much smaller. Our group is
strongly involved in experiments at the Bonn ELSA
(see http://wwwnew.hiskp.uni-bonn.de/cb/)
and the Mainz MAMI electron accelerators
(see http://wwwa2.kph.uni-mainz.de/A2/).
Both experiments use tagged photon beams and state-of the art electromagnetic
calorimeters for the detection of the decay products of the mesons.
The availability of polarized photon beams combined with polarized targets
opens a whole new field of experiments, which are highly sensitive to the
properties of nucleon resonances. Our group, in particular, has initiated a
very fruitful program concentrated on meson photoproduction of the
(quasi)-free neutron (loosely bound in the deuteron). In addition we
investigate the modifications of hadrons embedded in the nuclear medium
via the investigation of meson photoproduction off (heavy) nuclear targets.

In parallel to these experimental activities our group is involved in the
technical developments of the PANDA detector, which will be the main
working horse for the investigation of the strong interaction via
proton - antiproton collisions at the planned FAIR facility at GSI in the
next decade. During the last few years, we have developed key components for
the front-end electronics the electromagnetic calorimeter, which is
a central component of the detector. Currently, prototype construction and
tests are under way and construction of the first calorimeter sections will
start in 2009/2010 (see Technical Design Report for the PANDA Electromagnetic
Calorimeter http://arxiv.org/abs/0810.1216v1).