Rejection of α-particle background for neutrinoless double beta decay search with pixel detectors

Experiments searching for the neutrinoless double beta decay require a very low level of background. Most experiments aim for a background rate of about 10−4 to 10−3events/kg keV yr. α-particles can be an important part of the background since they occur as decay products of many isotopes in the natural decay chains. They are emitted with kinetic energies of a few MeV and therefore produce background at the Q-value of most double beta isotopes. In this publication we demonstrate experimentally that α-particle background can be reduced by about six orders of magnitude exploiting its topology of triggered pixels which is different from neutrinoless double beta decay of 116Cd.