HERA-B is a large-aperture high-rate spectrometer built for studies of collisions of 920 GeV protons with the nuclei of target wires positioned in the halo of the HERA proton beam. HERA-B was optimized to measure CP-violation in decays of B mesons into the so-called ``golden decay mode''.
This ambitious goal required picking each golden-decay event out from a background of 1011 hadronic interactions at a rate of 40 million interactions per second. This in turn required advances in radiation-hard technologies, the development of a sophisticated first level trigger and the construction of the first large integrated multi-level switch-based data acquisition and high-level trigger system.
The experiment is located at the proton-electron accelerator HERA at DESY in Hamburg, Germany. The collaboration consists of 32 institutes and about 250 collaborators from 13 countries.