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T: Fachverband Teilchenphysik

T 88: Niederenergie-Neutrinophysik und Suche nach Dunkler Materie III

T 88.1: Gruppenbericht

Mittwoch, 5. März 2008, 16:45–17:05, KGI-HS 1098

First results from Borexino — •Grzegorz Zuzel for the BOREXINO collaboration — Max-Planck-Institut für Kernphysik

In May 2007 the Borexino detector was successfully completed and the data taking began. The aim of the experiment, located in the underground laboratory of the LNGS in Italy, is to measure low energy (around 1 MeV) solar neutrinos in real time via elastic neutrino-electron scattering in liquid scintillator. To achieve that goal extremely high radio-purity of the scintillator had to be reached basing on a long R&D program. Data collected so far show that the background level in the detector is superior to the design specification. For U and Th we have measured <1E-17 g/g (1E-16 g/g was specified) and C14/C12 was found to be at the level of 1E-18 (as measured with the Counting Test Facility). Four Kr85 fast coincidences have been recorded in a 121-day live time period indicating probably a small air leak during filling. The main contamination of the scintillator comes from Po210 with the rate of about 60 counts/day/ton. A fit to the recorded energy spectra gives the Be7-neutrino rate of (47 +- 7{stat} +- 12{sys}) counts/day/100 t. This is in a very good agreement with the Standard Solar Model and neutrino oscillation with LMA-MSW parameters [1]. Present status of the experiment, data analysis and future plans will be discussed.

[1] C. Arpesella et al., Borexino Collaboration, Phys. Lett. B In Press, Corrected Proof, (2007)