THE 8B SOLAR NEUTRINO ANALYSIS IN BOREXINO AND SIMULATIONS OF MUON INTERACTION PRODUCTS IN BOREXINO AND DOUBLE CHOOZ

The present work deals with both 8B solar neutrino analysis in Borexino, and Monte Carlo (MC) simulation of cosmic muon interaction products in Borexino and Double Chooz. In Borexino, the 8B solar neutrino analysis was performed at the lowest energy thresholds ever reached: 3 and 2MeV. Setting the energy threshold at 3MeV required the study and development of removal techniques for cosmogenic isotopes. Decreasing the energy threshold down to 2MeV required a deep study of the external backgrounds affecting the Borexino core, and the development of precise MC tools to reproduce their radial and energy distributions. The measured rates, (0.22 ± 0.04stat ± 0.01syst) cpd/100t above 3MeV and (0.31 ± 0.04stat ± 0.01syst) cpd/100t above 2MeV, are compatible with the expectation based on the Standard Solar Model plus MSW-LMA oscillation solution. Borexino and Double Chooz experiments use liquid scintillator detectors, affected by cosmogenic contaminations from underground surviving muons. Many MC codes have been developed to describe muon interactions and subsequent hadronic cascades and neutron or isotope productions. Simulations through Geant4 and FLUKA were performed. The comparison with the Borexino data showed two important results concerning muon beam with mean energy around 270GeV. First, the neutron interactions are well reproduced by Geant4 and FLUKA. On the contrary, the hadronic shower development is underestimated, as proven by the disagreement with the cosmogenic isotope and neutron rates. Double Chooz data on cosmogenics rates will soon be available. They will allow MC/data comparison for a muon beam energy range of about 64GeV.