Commissioning of the HERA-B internal target: using the HERA proton ring as a B-factory

HERA-B is a fixed target experiment using the 920 GeV HERA proton storage ring to produce B-mesons. The internal target consists out of eight thin ribbons, which are positioned around the beam, and operates in the beam halo. An interaction rate of 40 MHz is required to achieve the primary goal – a significant CP measurement in the gold-plated B decay mode B0→J/ψKS0 within one year of data taking. The performance of the internal target has been studied in detail for several years. During the last two years the main effort was spent for a successful transition from a test setup to a continuous operational device and into the improvement of the efficiency. This paper reviews the requirements, the impacts and the performance of the HERA-B target.