The solar neutrino HELLAZ project

This is a status report of the HELLAZ project, in which a 20 bar He TPC is used to detect the recoil electrons coming from elastic scattering of solar neutrinos. Both the energy and direction (relative to the sun) are measured, allowing to reconstruct the neutrino energy. The measurement of direction of the very low energy electron is difficult. It requires to gather as much information as possible. Hence, it has been chosen to detect separately each individual ionization electron to get the maximum statistics which implies to have a gain in the end-cap detector of the TPC > 106, together with an X-Y capability. The R&D setup was moved a year ago from College de France, where it has been proven on one pixel that this gain is attainable, to Saclay, where a 10×10 cm2 TPC with 64×64 strips is setup.