Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth

Abstract

The solar neutrino experiment Borexino, which is located in the Gran Sasso underground laboratories, is in a unique position to study muon-induced backgrounds in an organic liquid scintillator. In this study, a large sample of cosmic muons is identified and tracked by a muon veto detector external to the liquid scintillator, and by the specific light patterns observed when muons cross the scintillator volume. The yield of muon-induced neutrons is found to be Y-n = (3.10 +/- 0.11) . 10(-4) n/(mu . (g/cm(2))). The distance profile between the parent muon track and the neutron capture point has the average value lambda = (81.5 +/- 2.7) cm. Additionally the yields of a number of cosmogenic radioisotopes are measured for N-12, B-12, He-8, C-9, Li-9, B-8, He-6, Li-8, Be-11, C-10 and C-11. All results are compared with Monte Carlo simulation predictions using the FLUKA and GEANT4 packages. General agreement between data and simulation is observed for the cosmogenic production yields with a few exceptions, the most prominent case being C-11 yield for which both codes return about 50% lower values. The predicted mu-n distance profile and the neutron multiplicity distribution are found to be overall consistent with data.