Commissioning of the BGO-OpenDipole setup at beamline S of ELSA

The new experimental BGO-OpenDipole setup will be assembled at the ELSA beamline S during 2009. It consists of the combination of an open-dipole forward spectrometer and the BGO Ball of the former GRAAL collaboration to cover the central angular region. This configuration is ideally suited to investigate the photoproduction of multiparticle final states with mixed charges. It extends the present Crystal-Barrel capabilities significantly towards strangeness and vector meson production, and, due to the trigger capability of the BGO readout, to quasifree production of neutral mesons off the neutron using a deuteron or He target. In addition it will allow nucleon polarization measurements in single-meson photoproduction. The main piece of the spectrometer is a large 90 t dipole magnet. Scintillating fiber detectors in front of the magnet and drift chambers behind it enable track and hence momentum reconstruction of charged particles. Combined with the time-of-flight from a large scintillator wall, particle ID is provided, enhanced through an aerogel Cherenkov detector. The BGO Ball detects charged and neutral particles, in particular photons. Moreover, it has high efficiency for neutrons. The whole setup will be taken into operation during the year 2010. Time for hall access is requested for the setup phase in 2009. The commissioning of the subdetectors and of the whole setup requires dedicated beamtimes in 2009 and 2010.