Abstract:

BOREXINO is a real-time solar neutrino detector which aims to measure the 7Be neutrino flux from the sun. Like all rare event experiments Borexino has to fight the background which mainly consists of internal contamination of the scintillator and the detector materials. Although being deep underground (3600 mwe) the external background from atmospheric muons is not negligible. Thus a water Cherenkov detector surrounding the spherical scintillation neutrino detector was designed in order to veto the muons crossing the detector. In this talk the design, simulation and installation of the Borexino outer detector will be discussed. Furthermore a method of suppressing the muon induced background by tracking the muon will be presented.