Status of Borexino experiment and Physics results with its Counting Test Facility (CTF)

Borexino is a solar neutrino experiment located under the Gran Sasso mountain in Italy. It is currently in the commissioning phase and will start taking data in 2007. Its main goal is to detect low-energy neutrinos coming from the sun in real-time, via the scattering reaction ν e − → ν e−. Borexino exploits 300 tons of liquid scintillator as active target for neutrinos and 2200 photomultiplier tubes mounted on a stainless steel sphere (d=14m) to view the scintillation light emitted by the recoil electron. In order to lower the experimental threshold down to 250 keV, it is necessary to keep unprecedented levels of radioupurity of the scintillator and of all the materials surrounding it. A prototype of Borexino, the Counting Test Facility (CTF) has been built and operated since 1994 to prove the capability to reach such levels of radiopurity. Besides its main goal of pilot experiment for Borexino, the high mass and high radiopurity of CTF have made it a unique detector to explore rare or forbidden processes with unprecedented sensitivity. Some of the physics results obtained in the last years with CTF are presented: they include limits on neutrino magnetic moment, electron lifetime, Pauli Exclusion Principle violation, nucleon decay and anti-neutrino flux from the sun.