New TeO2/NbSi detectors for rare event search

The present limitation for experiments looking for rare events, such as neutrinoless double beta decay (0 nu beta beta) and direct WIMPs detection, is the radioactive background and in particular its discrimination. When the search is based on the bolometric technique, near-surface events constitute a serious problem, due to full volume sensitivity of the detector; in fact for a 0 nu beta beta experiment they may cause signals close to the Q-value while for a dark matter (DM) experiment, which exploits ionization signal for particle identification, they may originate an incomplete charge collection simulating a nuclear recoil. We will describe a technique for the active suppression of the surface background which uses NbSi thin film thermometers acting as out-of-equilibrium phonon sensor. After very promising results obtained on germanium and sapphire bolometers, here we present some results on a small TeO2 one equipped with two NbSi films; in fact TeO2 is an interesting material for the search for 0 nu beta beta of Te-130. In particular we show that we are able to identify alpha surface events on TeO2 by pulse shape analysis with a good separation between bulk and surface events.